allows fbo to be used without shader in update() on RPi
removed uniqueShader conditional from endCustomShader, fixes display corruption on RPi when shaders used in draw()
Merge pull request #2886 from jvcleave/bugfix-ofGLProgrammableRenderer-uniqueShader

ofGLProgrammableRenderer fixes for RPi
added libmpg123-dev to install_dependencies.sh for armv6l
Merge pull request #2887 from jvcleave/bugfix-libmpg123-updated

added libmpg123-dev to install_dependencies.sh for armv6l
Merge branch 'master' of https://github.com/openframeworks/openFrameworks.git into rexgo