Some pretty brute-force compiler warning fixes

warning:
  narrowing conversion of ‘rect.FIFE::RectType<int>::w’ from
  ‘const int’ to ‘Uint16 {aka short unsigned int}’ inside { } is
  ill-formed in C++11 [-Wnarrowing]

Closes #789
 * Enhanced OpenGL backend. refs #822
Depth buffer was added and for that two new options. So a client can enable or disable depth buffer rendering with GLUseDepthBuffer. Additionally the value for the alpha test can be changed with GLAlphaTestValue. Note that SortingStrategy is ignored and some special light things may not work with depth buffer.
The OpenGLe backend is still available. If no one has objections, it may be removed.
Furthermore the static layer function was changed so that it should be possible to mix static with nonstatic layers. And it works without FBO, too. fixes #765
Merge pull request #824 from fifengine/t789

Some pretty brute-force compiler warning fixes
 * More work on OpenGL backend. refs #822
Merge branch 'master' of https://github.com/fifengine/fifengine
 * Removed VertexPointer and AlphaTest hacks. refs #822
 * Reduced overlay code size and added partial sorting. refs #822
Increase version to 0.4.0 for upcoming release.
 * Overlays now also use the alpha value of the client. refs #822
When using scons, if the fifechan module is build the files for it will now be also installed to python.
Fixed compiler warnings and an multicell pathfinder bug.
Add fix to build engine.h/cpp under macosx
Build fife using macosx
Fix typo
Fix more problems in the mac build script
Hopefully actually fail build when buildings fails
try to fix a build problem in engine.cpp
Fix stupid mistake in build file
Try to fix errors in mac build
Another small fix