testing: compile regexp only once The -test.run and -test.bench flags were compilng the regexp for ever test function, which was mucking up memory profiles.   Add a simple wrapper to save the compiled state so that the regexp is compiled only once for each flag.
testing: compile regexp only once
The -test.run and -test.bench flags were compilng the regexp for ever test
function, which was mucking up memory profiles.   Add a simple wrapper
to save the compiled state so that the regexp is compiled only once for
each flag.

R=rsc
CC=golang-dev
http://codereview.appspot.com/4274063
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go