Fix L-BFGS mex function

[lostella]

As pointed out by @Zilleplus here the L-BFGS mex function should be fixed as in here in order to avoid compatibility problems: we should be using mwSize in place of size_t for specifying array dimensions.

[MelisWillem]

We should just copy over lbfgs.c from ForBeS, because some of the parameters that where put to size_t should still be int to be safe. I checked all this and fixed it in ForBeS...

[lostella]

Yep, I just opened this to pin down the issue

[MelisWillem]

already made pull request #3 also changed setup, still needs to be tested on Matlab tough