Fix quoting and typos.

Also set gl_dlopen_path before using it.
--- configure.ac.orig	2020-09-01 21:37:12.000000000 -0500
+++ configure.ac	2020-09-01 23:48:58.000000000 -0500
@@ -76,7 +76,7 @@
 
 dnl to avoid misleading error messages later
 AS_IF([ test "x${PKG_CONFIG}" = x ],
-	[AC_MSG_ERROR([required pkg-config utility not found.])],
+	[AC_MSG_ERROR([required pkg-config utility not found])],
 	[])
 
 #
@@ -118,6 +118,19 @@
 AC_DEFINE_UNQUOTED([CPUSTRING], "${host_cpu}", [Canonical CPU identification])
 AC_DEFINE_UNQUOTED([BUILDSTRING], "${host_os}", [Canonical OS identification])
 
+dnl ---- Darwin search for OpenGL library
+dnl  (ref: dlopen(3) for Mac OS X.)
+dnl  See Darwin notes above.
+gl_dlopen_path=default
+AS_IF([ test "x${unix_host}" = xdarwin ],[
+	AC_MSG_CHECKING([for GL_LIBDIR (location of libGL.dylib)])
+	AC_ARG_VAR( GL_LIBDIR, [directory containing libGL.dylib])
+	AC_MSG_RESULT([${GL_LIBDIR}])
+	AS_IF([ test "x${GL_LIBDIR}" = x ],[
+		gl_dlopen_path=${x_libraries}],[
+		gl_dlopen_path=${GL_LIBDIR}])
+])
+
 dnl
 dnl Set names of dlopened libraries for config.h
 dnl The Darwin configuration attempts to conform to MacPorts.
@@ -137,7 +150,7 @@
 		])
 		AC_DEFINE_UNQUOTED([OPENAL_DRIVER],
 			["@PREFIX@/lib/libopenal.dylib"],
-			[OpenAl dynamic lib path])
+			[OpenAL dynamic lib path])
 		],[
 		AC_DEFINE_UNQUOTED([OPENGL_DRIVER],
 			["libGL.so.1"],[OpenGL shared lib name])
@@ -229,27 +242,14 @@
 dnl ---- pthread (client)
 AX_PTHREAD([],
 	[AC_MSG_ERROR(
-		["Required pthreads support not found (or invalid CFLAGS)."])])
+		[required pthreads support not found (or invalid CFLAGS)])])
 dnl This might be a workaround for DSO missing pthread library error:
 AS_IF([ test "x${PTHREAD_LIBS}" = x ],[PTHREAD_LIBS="-pthread"])
 
 
-dnl ---- Darwin search for OpenGL library
-dnl  (ref: dlopen(3) for Mac OS X.)
-dnl  See Darwin notes above.
-gl_dlopen_path=default
-AS_IF([ test "x${unix_host}" = xdarwin ],[
-	AC_MSG_CHECKING([for GL_LIBDIR (location of libGL.dylib)])
-	AC_ARG_VAR( GL_LIBDIR, [directory containing libGL.dylib])
-	AC_MSG_RESULT([${GL_LIBDIR}])
-	AS_IF([ test "x${GL_LIBDIR}" = x ],[
-		gl_dlopen_path=${x_libraries}],[
-		gl_dlopen_path=${GL_LIBDIR}])
-])
-
 dnl ----  X11 (client)
 PKG_CHECK_MODULES([X11],[x11],,[
-	AC_MSG_ERROR(["Required Xll library not found"])
+	AC_MSG_ERROR([required X11 library not found])
 ])
 
 dnl ---- xf86vm (client)
@@ -338,26 +338,26 @@
 
 dnl ---- libjpeg (client)
 AC_SEARCH_LIBS([jpeg_read_header],[jpeg],,[
-	AC_MSG_ERROR(["Required jpeg library not found"])
+	AC_MSG_ERROR([required jpeg library not found])
 ])
 
 dnl ---- libcurl (client)
 PKG_CHECK_MODULES([LIBCURL],[libcurl],,[
-	AC_MSG_ERROR(["Required cURL library not found"])
+	AC_MSG_ERROR([required cURL library not found])
 ])
 
 dnl ---- ogg, vorbis, vorbisfile (client)
 PKG_CHECK_MODULES([OGG],[ogg],,[
-	AC_MSG_ERROR(["Required Ogg libraries not found"])
+	AC_MSG_ERROR([required Ogg libraries not found])
 ])
 
 PKG_CHECK_MODULES([VORBIS],[vorbis vorbisfile],,[
-	AC_MSG_ERROR(["Required Vorbis libraries not found"])
+	AC_MSG_ERROR([required Vorbis libraries not found])
 ])
 
 dnl ---- freetype2 (client)
 PKG_CHECK_MODULES([FREETYPE2],[freetype2],,[
-	AC_MSG_ERROR(["Required FreeType2 library not found"])
+	AC_MSG_ERROR([required FreeType2 library not found])
 ])
 
 dnl
@@ -442,29 +442,29 @@
 jpeglib_h_found=no
 AC_CHECK_HEADERS([jpeglib.h jpeg/jpeglib.h],[ jpeglib_h_found=yes ])
 AS_IF([ test "x${jpeglib_h_found}" = xno ],
-	[AC_MSG_ERROR("Required JPEG header file, jpeglib.h, not found.")])
+	[AC_MSG_ERROR([required JPEG header file, jpeglib.h, not found])])
 
 dnl ---- OpenAL (client)
 openal_h_found=no
 AC_CHECK_HEADERS([AL/al.h al.h OpenAL/al.h],[ openal_h_found=yes ])
 AS_IF([ test "x${openal_h_found}" = xno ],
-	[AC_MSG_ERROR("Required OpenAL header file, al.h, not found.")])
+	[AC_MSG_ERROR([required OpenAL header file, al.h, not found])])
 
 openalc_h_found=no
 AC_CHECK_HEADERS([AL/alc.h alc.h OpenAL/alc.h],[ openalc_h_found=yes ])
 AS_IF([ test "x${openalc_h_found}" = xno ],
-	[AC_MSG_ERROR("Required OpenAL header file, alc.h, not found.")])
+	[AC_MSG_ERROR([required OpenAL header file, alc.h, not found])])
 
 dnl ---- OpenGL (client)
 AC_CHECK_HEADERS([GL/gl.h],,
-	[AC_MSG_ERROR("Required OpenGL header file, gl.h, not found.")])
+	[AC_MSG_ERROR([required OpenGL header file, gl.h, not found])])
 AC_CHECK_HEADERS([GL/glx.h],,
-	[AC_MSG_ERROR("Required OpenGL header file, glx.h,  not found.")])
+	[AC_MSG_ERROR([required OpenGL header file, glx.h, not found])])
 
 dnl ---- ODE (client)
 AS_IF([ test "x$system_libode" = "xyes"],[ 
 	AC_CHECK_HEADERS([ode/ode.h],,
-		[AC_MSG_ERROR("with-system-libode: Required ODE header file, ode.h, not found.")]
+		[AC_MSG_ERROR([with-system-libode: required ODE header file, ode.h, not found])]
 		[],
 		[
 #define dDOUBLE