Re: Add some aliases for re-related functions

[Philippe Vaucher]

Without that I have to C-h d "regexp posix" and curse because it returns no result (Eli <--- please fix this), then search for C-h d posix and only then find it.

FYI none of "posix regexp", "posix search" or "posix forward" in C-h d returns any result (expected to find `posix-search-forward` with the later).