cvx_solver_shim.m: extract the version number from a test ECOS run

Here you go. Now that ECOS prints out the version number, I've added code to extract it during cvx_setup. 

As an alternative, I could just read the number right out of ../include/ecos.h, I suppose. I do something like that for SeDuMi. This might actually be better anyway, since Octave can't handle evalc. (Not that you're supporting octave yet.)