libsvm compilation in Matlab2016a

[patrickkwang]

prtSetupMex fails with

error: conflicting types for ‘mwIndex’
typedef int mwIndex;

for each .c file in +prtExternal/+libsvm

Libsvm now has a Github page: https://github.com/cjlin1/libsvm/tree/master/matlab
and adopting the latest version seems to solve this problem. Specifically,
#ifdef MX_API_VER
#if MX_API_VER < 0x07030000
typedef int mwIndex;
#endif
#endif
replaces
#if MX_API_VER < 0x07030000
typedef int mwIndex;
#endif

More testing is required to verify this solution. We should also determine if there is a better way of including dependencies on external software like this.