Add ccache support

[collin walker]

supporting ccache can significantly speed up build times. This is very useful for situations where you are tweaking a build configuration and end up rebuilding multiple times.

https://stackoverflow.com/questions/1815688/how-to-use-ccache-with-cmake

Using the above link, I added the following lines between the
"Find google Perftoos" section and the "Find MKL" section in CMakeLists.txt

find_program(CCACHE_FOUND ccache)  
if(CCACHE_FOUND)  
    set_property(GLOBAL PROPERTY RULE_LAUNCH_COMPILE ccache)  
    set_property(GLOBAL PROPERTY RULE_LAUNCH_LINK ccache)  
endif(CCACHE_FOUND)  

[Frank Dellaert]

Added by PR #357