Adds tests for pm-updatestatus.
Rename update_info engine to update_status and convert into OO.
Change inheritance pattern in StatusInfoDrupal classes.
Use backend results instead of table output in pm-updatestatus tests.
Reduce duplicity of code in update_status engine, and decouple from constants declared in update.module.
Simplify checking of version-specific requests in pm-updatestatus.
Merge pull request #911 from jonhattan/update_info-oo

Rename update_info engine to update_status and convert into OO