Convert sed(1) syntax to be compatible with FreeBSD and OpenBSD

Convert sed(1) syntax to be compatible with FreeBSD and OpenBSD

BSD regex library doesn't support extended RE escapes (e.g. \+) and
shorthand character classes (e.g. \s, \S) and SVR4-style word
delimiters[1] (on DragonFly and NetBSD). Both GNU and BSD sed support
-E and -r to enable extended RE but OS X still lacks -r.

[1] https://www.illumos.org/issues/516

Reviewed-by: Eric Engestrom <eric.engestrom@imgtec.com>
Tested-by: Eric Engestrom <eric.engestrom@imgtec.com> (GNU sed)