autoconf: Consistently use xlib for the driver name

Brian suggested that there should be more consistency using xlib vs. x11
in the configure script. Changed the options and variables to suit.

configure.ac

@@ -180,17 +180,17 @@ AC_SUBST(GLW_LIB_NAME)
 AC_SUBST(OSMESA_LIB_NAME)
 
 dnl
-dnl Driver configuration. Options are x11 (Xlib), dri and osmesa right now.
+dnl Driver configuration. Options are xlib, dri and osmesa right now.
 dnl More later: directfb, fbdev, ...
 dnl
 AC_ARG_WITH(driver,
     [AS_HELP_STRING([--with-driver=DRIVER],
-        [driver for Mesa: x11,dri,osmesa @<:@default=x11@:>@])],
+        [driver for Mesa: xlib,dri,osmesa @<:@default=xlib@:>@])],
     mesa_driver="$withval",
-    mesa_driver="x11")
+    mesa_driver="xlib")
 dnl Check for valid option
 case "x$mesa_driver" in
-xx11|xdri|xosmesa)
+xxlib|xdri|xosmesa)
     ;;
 *)
     AC_MSG_ERROR([Driver '$mesa_driver' is not a valid option])
@@ -204,7 +204,7 @@ SRC_DIRS="mesa"
 GLU_DIRS="sgi"
 WINDOW_SYSTEM=""
 case "$mesa_driver" in
-x11)
+xlib)
     DRIVER_DIRS="x11"
     ;;
 dri)
@@ -279,7 +279,7 @@ fi
 
 dnl We need X for xlib and dri, so bomb now if it's not found
 case "$mesa_driver" in
-x11|dri)
+xlib|dri)
     if test "$no_x" = yes; then
         AC_MSG_ERROR([X11 development libraries needed for $mesa_driver driver])
     fi
@@ -290,11 +290,11 @@ dnl
 dnl libGL configuration per driver
 dnl
 case "$mesa_driver" in
-x11)
+xlib)
     if test "$x11_pkgconfig" = yes; then
-        PKG_CHECK_MODULES(X11GL, x11 xext)
-        X11_INCLUDES="$X11_INCLUDES $X11GL_CFLAGS"
-        GL_LIB_DEPS="$X11GL_LIBS"
+        PKG_CHECK_MODULES(XLIBGL, x11 xext)
+        X11_INCLUDES="$X11_INCLUDES $XLIBGL_CFLAGS"
+        GL_LIB_DEPS="$XLIBGL_LIBS"
     else
         # should check these...
         X11_INCLUDES="$X11_INCLUDES $X_CFLAGS"
@@ -342,7 +342,7 @@ AC_SUBST(GL_LIB_DEPS)
 dnl
 dnl More X11 setup
 dnl
-if test "$mesa_driver" = x11; then
+if test "$mesa_driver" = xlib; then
     DEFINES="$DEFINES -DUSE_XSHM"
 fi
 
@@ -489,21 +489,21 @@ AC_SUBST(DRI_LIB_DEPS)
 dnl
 dnl OSMesa configuration
 dnl
-if test "$mesa_driver" = x11; then
-    default_x11_osmesa=yes
+if test "$mesa_driver" = xlib; then
+    default_xlib_osmesa=yes
 else
-    default_x11_osmesa=no
+    default_xlib_osmesa=no
 fi
-AC_ARG_ENABLE(x11-osmesa,
-    [AS_HELP_STRING([--disable-x11-osmesa],
-        [enable OSMesa on X11 libGL @<:@default=enabled for x11 driver@:>@])],
-        x11_osmesa="$enableval",
-        x11_osmesa="$default_x11_osmesa")
-if test "x$x11_osmesa" = xyes; then
-    if test "$mesa_driver" = x11; then
+AC_ARG_ENABLE(xlib-osmesa,
+    [AS_HELP_STRING([--disable-xlib-osmesa],
+        [enable OSMesa on Xlib libGL @<:@default=enabled for xlib driver@:>@])],
+        xlib_osmesa="$enableval",
+        xlib_osmesa="$default_xlib_osmesa")
+if test "x$xlib_osmesa" = xyes; then
+    if test "$mesa_driver" = xlib; then
         DRIVER_DIRS="$DRIVER_DIRS osmesa"
     else
-        AC_MSG_ERROR([Can only enable OSMesa on libGL for X11])
+        AC_MSG_ERROR([Can only enable OSMesa on libGL for Xlib])
     fi
 fi
 
@@ -789,7 +789,7 @@ dnl Driver info
 echo ""
 echo "        Driver:          $mesa_driver"
 case "$mesa_driver" in
-x11|osmesa)
+xlib|osmesa)
     if echo "$DRIVER_DIRS" | grep 'osmesa' >/dev/null 2>&1; then
         echo "        OSMesa:          lib$OSMESA_LIB"
     else