Suppressed uninterested error messages.

* compilers.jam: Suppressed uninterested error messages printed by `gcc-ar`,
                 `gcc-ranlib` and `gcc-nm`.
Fixed a comment.

* compilers.jam: Fixed a comment.
Merge pull request #112 from Cryolite/fix/gccBinutilsWrappers

Suppressed uninterested error messages.