gcc49 4.9.1

Update to latest stable release, use HTTPS on homepage URL, change, single quotes to double, change dependencies to the regular formulas instead of particular versions.
The gcc formulae in hombrew-versions are pinned to the "gcc infrastructure" versions of these dependencies (see e.g. http://www.mirrorservice.org/sites/sourceware.org/pub/gcc/infrastructure/), so I think we want to leave them be unless there is a compelling reason not to.