Make Production Monitor play nice with Update module

This is a great module, but the fact that it doesn't play nice with the Update module is a huge drawback.

• Can't run modules like the Apps or DRD modules that have a hard dependency on Update
• Can't run drush up so you have to constantly turn modules on and off to be able to run drush on dev, which means that dev is not a true mirror of production.
• A requirement to disable a core module that is fundamental to the Drupal security model just seems much too heavy handed

There are other minor issues perhaps.

As near as I can tell, the only conflict is that production monitor redefines constants that are also defined by update in order to avoid loading the whole update module just to run the production monitor checks.

Rather than having a hard requirement that update be disabled (implemented currently by hook_requirements() in the install file) it seems like it would make a lot more sense to simply check if the update module is enabled and, if so, don't redefine the constants.

I have been doing this with a simple patch and it works fine. I have no conflict with the update module that I've experienced so far.

Simple patch follows once I submit this and get an issue number.