pullrequest: disable pr on commits that dont share ancestor

logging: log the original error when a merge failure occurs

feature: Go To switcher now searches commit hashes as well

api: gracefully handle errors on repos that are damaged or missing from filesystem.

authn: Data migration for renaming 'container' to 'headers'. Rename the 'auth_plugins' setting and all 'auth_container_%s' settings.

authn: Renamed auth_container -> auth_headers

login: Fix login redirection when came_from not set.

login: Moved method out of login view.

setup: Remove DB setting entry from rhodecode setup code.

authn: Add whitespace stripping to authentication plugin settings.