We allow certain special regex characters in formula names, and if
those aren't escaped when interpolating them into a regex, they'll be
interpreted as special regex characters.
This can cause regex compile errors on Ruby 1.8 (for example, with
"libxml++3", which has nested match characters), and more subtle
matching bugs in general.
Refs an issue surfaced in Homebrew/homebrew#48744.
ClosesHomebrew/homebrew#49005.
Signed-off-by: Misty De Meo <mistydemeo@gmail.com>
