Using GTK+2 as default

GTK+3 is still not mature enough.

Author: mowgli

README.md

@@ -113,7 +113,7 @@ Or: `git clone http://www.geeqie.org/git/geeqie.git`
 List compile options: `./autogen.sh --help`
 
 Common options:
-`./autogen.sh --disable-gtk3`,
+`./autogen.sh`,
 
 Compilation: `./autogen.sh [options]; make -j<no. of cpu cores> `
 
@@ -146,16 +146,16 @@ And either the ChangeLog file or [Geeqie ChangeLog](http://geeqie.org/cgi-bin/gi
 ## Requirements
 
 ### Required libraries:
-    GTK+ 3.00
-        www.gtk.org
-        enabled by default
-        disable with configure option: --disable-gtk3
-    or
     GTK+ 2.20
-        disabled by default when GTK+3 libraries are found.
-        enable with configure option: --disable-gtk3
+        enabled by default even when GTK+3 libraries are found.
+        disable with configure option: --enable-gtk3
         optional items map display and GPU acceleration are not available
         with GTK2
+    or
+    GTK+ 3.00
+        www.gtk.org
+        disabled by default when GTK+2 libraries are found.
+        enable with configure option: --enable-gtk3
 
         Note: GTK+3 is still somehow experimental. It is needed for some
         features but we have several complains about the GTK+3 usability.

configure.in

@@ -198,16 +198,11 @@ else
 fi
 
 AM_PATH_GLIB_2_0(2.24.0,,AC_MSG_ERROR(GLIB >= 2.24.0 not installed.))
-AC_ARG_ENABLE([gtk3], AC_HELP_STRING([--disable-gtk3], [use gtk2 instead of gtk3]),[gtk3="${enableval}"], [gtk3=m4_ifdef([AM_PATH_GTK_3_0], [auto], [no])])
+AC_ARG_ENABLE([gtk3], AC_HELP_STRING([--enable-gtk3], [use gtk3 instead of gtk2]),[gtk3="${enableval}"], [gtk3=m4_ifdef([AM_PATH_GTK_3_0], m4_ifdef([AM_PATH_GTK_2_0], [no], [auto]), [no])])
 
 if test x$gtk3 == xyes; then
     AC_MSG_WARN("Gtk3 enabled")
     m4_ifdef([AM_PATH_GTK_3_0], [AM_PATH_GTK_3_0(3.0.0,,AC_MSG_ERROR(GTK+ >= 3.0.0 not installed.))])
-else
-    if test x$gtk3 != xno; then
-       AC_MSG_WARN("Gtk3 is preferred...")
-       m4_ifdef([AM_PATH_GTK_3_0], [AM_PATH_GTK_3_0(3.0.0,,[gtk3=no])])
-    fi
 fi
 
 if test x$gtk3 == xno; then