fixup issue 767 & func.cc cleanup
1) fixed last cases of duplicate calls to getArgValue() in builtin_lookup() and instantiate();
2) make sin_degrees() & cos_degrees() separate functions to use in other parts of code;
3) cleaned most of gcc warnings in func.cc
Merge pull request #823 from tim-caper/func.cc

fixup issue 767 & func.cc cleanup