X11 build fixups

- fixed -Werror=misleading-indentation warning
- fixed -Werror=nonnull-compare warning on xll and QT builds
- PNG_LIBPNG_VER backward compatibily changes
- giflib backward compatibily changes
- resolved some undefs for X11 build
- silenced some small compile warnings in JGE Makefile
- added -DTIXML_USE_STL to remaining build types (PSP had it added)
- fixed x11 Boost incompatibility issue part of #548
- reworked PrecompiledHeader.h platforms used

JGE/src/JFileSystem.cpp

@@ -16,9 +16,14 @@ User folder is the only one that is really needed to guarantee both read and wri
 The content that users should not be touching.
 */
 
-#ifndef PSP
+#if defined (ANDROID)
 #include "PrecompiledHeader.h"
-#endif //PSP
+#endif //ANDROID
+
+#if defined (LINUX)
+#include "../../projects/mtg/include/PrecompiledHeader.h"
+#endif //LINUX
+
 
 #ifdef WIN32
 #pragma warning(disable : 4786)