Fix build with configure --enable-cairo --enable-cairoext.

Add missing #include <config.h>, see this report in fltk.general:

  https://groups.google.com/forum/#!topic/fltkgeneral/x80qQ6wt0s4


git-svn-id: file:///fltk/svn/fltk/branches/branch-1.4@12123 ea41ed52-d2ee-0310-a9c1-e6b18d33e121

CHANGES

@@ -1,18 +1,26 @@
-Changes in FLTK 1.4.0					RELEASED: ??? ?? 2017
+Changes in FLTK 1.4.0					Released: ??? ?? 2017
 
+  General Information about this Release
 
-  New features and extensions
+  - FLTK 1.4.0 is based on FLTK 1.3.4 (released Nov 15 2016),
+    see CHANGES_1.3 for more information.
 
   - CMake is the primary supported build system in FLTK 1.4.0 and later.
     CMake can be used to generate Makefiles, IDE project files, and
     several other build systems by using different "generators" provided
     by CMake (for instance Ninja, CodeBlocks, Eclipse, KDevelop3, etc.).
     See README.CMake.txt for more information.
-    autoconf/configure is still supported by the FLTK team for backwards
+
+  - autoconf/configure is still supported by the FLTK team for backwards
     compatibility with older systems that lack CMake support.
 
 
-  New configuration options (ABI version)
+  New Features and Extensions
+
+  - (add here)
+
+
+  New Configuration Options (ABI Version)
 
   - FLTK's ABI version can be configured with 'configure' and CMake.
     See documentation in README.abi-version.txt.
@@ -23,14 +31,17 @@ Changes in FLTK 1.4.0					RELEASED: ??? ?? 2017
   - None. FLTK 1.4.0 has a new ABI, breaking 1.3.x ABI.
 
 
-  Other improvements
+  Other Improvements
 
   - (add here)
 
 
-  Bug fixes
+  Bug Fixes
 
   - (add here)
+  - Fix build with configure --enable-cairo --enable-cairoext,
+    see this report in fltk.general:
+    https://groups.google.com/forum/#!topic/fltkgeneral/x80qQ6wt0s4
 
 
   Removed Features
@@ -40,7 +51,6 @@ Changes in FLTK 1.4.0					RELEASED: ??? ?? 2017
     See README.CMake.txt for more information.
 
 
-
 Changes in FLTK 1.3
 
   See CHANGES_1.3

src/Fl_Window.cxx

@@ -20,6 +20,8 @@
 // This is the system-independent portions.  The huge amount of 
 // crap you need to do to communicate with X is in Fl_x.cxx, the
 // equivalent (but totally different) crap for MSWindows is in Fl_win32.cxx
+
+#include <config.h>
 #include <FL/Fl.H>
 #include <FL/x.H>
 #include <FL/Fl_Window_Driver.H>