-Add the -DUSE_PNG compiler flag to all build targets in the CodeBlocks project file.

git-svn-id: http://odamex.net/svn/root/trunk@4588 b0bcef46-2027-0410-bd56-ab726e9a1d04
-Fix a compilation issue with m_ostring.h

git-svn-id: http://odamex.net/svn/root/trunk@4589 b0bcef46-2027-0410-bd56-ab726e9a1d04