Replace xtext's transparency with full window transparency

Xtext's transparency barely worked on windows, didn't work on any modern
linux wm and used fake transparency.
This uses gtk's built in window opacity that works on more systems and
is real transparency.
Text area only transparency may return with a transition to cairo, if it
works on Windows.

configure.ac

@@ -49,7 +49,6 @@ AH_VERBATIM([USE_LIBCANBERRA],[#undef USE_LIBCANBERRA])
 AH_VERBATIM([USE_IPV6],[#undef USE_IPV6])
 AH_VERBATIM([USE_OPENSSL],[#undef USE_OPENSSL])
 AH_VERBATIM([USE_PLUGIN],[#undef USE_PLUGIN])
-AH_VERBATIM([USE_XLIB],[#undef USE_XLIB])
 AH_VERBATIM([USE_SIGACTION],[#undef USE_SIGACTION])
 AH_VERBATIM([USING_FREEBSD],[#undef USING_FREEBSD])
 AH_VERBATIM([USING_LINUX],[#undef USING_LINUX])
@@ -100,10 +99,6 @@ AC_ARG_ENABLE(textfe,
 	[AS_HELP_STRING([--enable-textfe],[build the text frontend (default: no)])],
         textfe=$enableval, textfe=no)
 
-AC_ARG_ENABLE(xlib,
-	[AS_HELP_STRING([--disable-xlib],[disable use of xlib (for non X11 systems)])],
-        xlib=$enableval, xlib=yes)
-
 AC_ARG_ENABLE(python,
 	[AS_HELP_STRING([--enable-python=pythonversion],[build the python plugin; possible values: "python2", "python3" or specific such as "python3.3" (default on, python2)])],
         python=$enableval, python=python2)
@@ -214,19 +209,6 @@ fi
 GUI_LIBS="$GUI_LIBS $GTK_LIBS"
 GUI_CFLAGS="$GUI_CFLAGS $GTK_CFLAGS -DG_DISABLE_SINGLE_INCLUDES -DGDK_PIXBUF_DISABLE_SINGLE_INCLUDES -DGTK_DISABLE_SINGLE_INCLUDES"
 
-dnl *********************************************************************
-dnl ** XLIB *************************************************************
-dnl *********************************************************************
-
-if test "$xlib" = yes; then
-	AC_DEFINE(USE_XLIB)
-	if test "$system" = "SunOS"; then
-		LIBS="$LIBS -L/usr/openwin/lib -lX11"
-	else
-		AC_CHECK_LIB(X11, XSetWMHints)
-	fi
-fi
-
 dnl *********************************************************************
 dnl ** PERL *************************************************************
 dnl *********************************************************************