Fix CMake for PNG (with the quotation mark, the "optimized/debug" will be misinterpreted).
Merge pull request #947 from yangyanli/fix_cmake_png

Fix CMake for PNG
Fix compiling on VS2012.
Fix an issue with PCLVisualizer producing empty screenshots
Fix style.
Merge pull request #956 from taketwo/fix-954

Fix an issue with PCLVisualizer producing empty screenshots
Merge pull request #955 from yangyanli/fix_compiling_vs2012

Fix compiling on VS2012.