Linux standalone: Include locale files in the bundle, and generate locale definition files for the locales in use when starting runshell.

Currently only done for utf-8 locales because the charset can easily be
told for those. Other locales don't include the charset in their name.

The locale definition is generated under git-annex.linux/locales.
So, this only works if the user can write there.

If locale generation fails for any reason, it's silently skipped.

The git-annex-standalone.deb installs the bundle under /usr, so this locale
generation won't work for non-root users.