Ryzom

This patch includes everything that i had to change to get r1575 to build and run snowballs client on mac os using macports

• added /opt/local/ pathes in some cmake find modules (for macports)
• removed -lrt flag for mac builds, needed functions are in libSystem.dyld according to this post
  http://lists.apple.com/archives/unix-porting/2008/Oct/msg00001.html
• added the png include path variable in lots on cmakelists
• added the .dyld library file ending in dynloadlib.cpp for mac systems
• adjusted the al include path in stdopenal.h for mac systems
• some adjustments for the opengl driver build config
• added nelnet to the logic build config
• added driver/sound_driver.cpp driver/buffer.cpp to sound source list