Upgrade script : Should throw a fatal error if version number in database is GREATER than version in the downloaded codebase

The upgrade script compares the version stored in the site database (civicrm_domain.version) to the version in the newly downloaded codebase (the one that the user is upgrading TO) - read from civicrm-version.txt. Currently, if the DB version is >= the "new" code version - it skips the upgrade process and gives this message to the user:

"Your database has already been upgraded to CiviCRM %1" - where %1 is the version from version.txt

However, we've had a few situations where the DB version has been an unexpected value - e.g. 2.11 - and the >= code has returned true - so no upgrade happened and the user thought everything was fine.

Given that there is no expected situation were the DB version is GREATER than the new code version, this condition should throw a fatal error rather than just skipping the upgrade:

"Your database is marked with an unexpected version number: %1. The automated upgrade to version %2 can not be run - and the %2 codebase may not be compatible with your database state. You will need to determine the correct version corresponding to your current database state. The database tools utility at %3 may be helpful. You may want to revert to the codebase you were using prior to beginning this upgrade until you resolve this problem."