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

projects/mtg/wagic.pri

@@ -9,6 +9,7 @@ unix:!*macx*:QMAKE_CXXFLAGS += -Wno-unused-but-set-variable
 unix|*macx*:QMAKE_CXXFLAGS += -Wno-unused-value
 unix:!*macx*:QMAKE_CXXFLAGS += -Wno-unused-local-typedefs
 unix:!*macx*:!maemo5:!symbian:QMAKE_CXXFLAGS += -Werror
+unix|macx:QMAKE_CXXFLAGS += -Wno-nonnull-compare
 
 windows:DEFINES += _CRT_SECURE_NO_WARNINGS
 windows|winrt:DEFINES += NOMINMAX