Merge branch 'skip-gettext-when-possible'

This topic branch allows us to skip the gettext initialization
when the locale directory does not even exist.

This saves 150ms out of 210ms for a simply `git version` call on
Windows, and it most likely will help scripts that call out to
`git.exe` hundreds of times.

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho