Issue #2373923 by griz - https redirect problem with Nginx

Sync with Apache config required.
Revert "Issue #2373923 by griz - https redirect problem with Nginx"

This reverts commit 3c5c0d4a908fee1b69670d9681cf6083ce18a0df.
Nginx: proper sync with Apache redirects.
Sync new lines.
Nginx: Remember real site name in $main_site_name and MAIN_SITE_NAME.
Nginx: Simplify imagecache/styles support.
Issue #2358977 by mrP - [nginx] Aegir redirection to non-install url leads to sites/$server_name/files 404 errors.
Merge branch 'refs/heads/6.x-2.x' into 2.3.x-dev