Merge pull request #229 from erwincoumans/master

add fileOpenDialog selector (Win/Mac/Linux), CMake remote CMAKE_INSTALL_PREFIX,fix support for dynamic loading of X11 functions
Merge pull request #230 from erwincoumans/master

remove BUILD_MULTITHREADING option from CMakeLists.txt
Merge pull request #231 from erwincoumans/master

stringify unified between linux and mac