Update solveCobraMILP.m

Amended code to make cplex_direct solver accesible through CPLEXMILP m-file and CPLEX C-interface. Actually, with the lack of this facility, earlier many useful functions such OptKnock, GDLS, FBA and FVA with loops removed could not be implemented with a cplex_direct solver. So, hope these amendments are useful.
Merge pull request #28 from meiya-laksh/patch-2

Update solveCobraMILP.m