Update WinSparkle.
Add Open In Editor button to file viewer.

Fixes #520.
Xcode 5 fix: hardcode path to gsed in /usr/local/bin.
More gettext build hacks: prevent moopp from running.

Fix yet another problem with gettext's makefiles: it relies on
timestamps alone to avoid running a fragile developer-only tool, moopp,
that requires GNU sed and won't allow itself to be configured via
Autoconf (as other pieces requiring GNU sed are).

I hate this thing.