Patches for OS X and clang, plus some other cleanup

This pull request contains most of the patches I use for the Mac OS X Fink package of Singular, mostly to fix compatibility issues with clang. It also silences a few warnings, and fixes some typos here and there.

There is one more change I make in the Fink package which I did not include here: That is the removal of -fno-implicit-templates. I did not include it because right now, (a) I don't quite recall what the precise problems where with it (probably simply that clang did not support it back than?), and (b) I assume you have a reason to use it in general, so you may not want to remove it by default everywhere.