Rename strtoi/strtof -> stoi/stof to match C++11 nomenclature

I was just reading up on C++11 and see that they've added stoi and stof.  Since we haven't done an official release with the new strtoi/strtof functions I added a week or so ago, I think we should rename to match C++11.

Just in case somebody has written and compiled a shader using the "old" names, I've added a little mechanism that lets us easily alias opcode names for just such a back-compatibility issue.  So with this in place, we have full back-compatibility of oso's, even if one was compiled during the couple unreleased weeks where the names were different.  But going forward, everybody should use stoi/stof.