Check for correct version.php numbers in pre-commit script

Mahara's version number policy for DB versions in version.php files is pretty simple:

1. in a _STABLE branch, a commit should only increment the version (whether for core or a plugin) by 1
2. in the master branch, a commit should increment the version to the day's date followed by 00

Since this is so simple, and we've recently had a mistake from it being manually checked, it's a perfect candidate to add to our pre-commit checks. The logic can be as follows:

IF you're modifying a version.php file && changing its $config->version value THEN
    IF the branch ends with "_STABLE" THEN
         Make sure the $config->version is being incremented by 1.
    ELSE
         Make sure the $config->version is higher than the old value, and ends with 00, and is less than or equal to today's date.

In some cases you might want to increment a version number on the master branch by 1 (like if you're pushing through multiple commits on the same day). But that's okay, that's what bypassing the pre-commit hook is for. ;)