Bash-specific performance by avoiding sed

[Mike Gran]

Hello libtool,

I don't know if y'all saw this blogpost where a guy pushed
the sed regular expression handling into bash-specific
regular expressions when bash was available.  He claims
there's a significant performance improvement because of
reduced forking.

http://harald.hoyer.xyz/2015/03/05/libtool-getting-rid-of-180000-sed-forks/

-Mike Gran