mex_compile_ros: Compile using existing system libraries

For system with 64-bit MATLAB, you can try out compiling the MEX files using existing system libraries. I was able to compile in this fashion and run the example on Ubuntu 12.04 with Matlab R2013a (Student Edition). (This is after having replaced MATLAB's copies of `libstdc++*`)

Of course, users run the risk of random errors given the different library versions, but this is for the impatient risk takers :P