Spellchecked /includes directory

* Ran spell-checker over code comments in /includes/
* A few spellchecking fixes for wfDebug() calls

Found one very strange (NOOP?) line in Linker.php - see "TODO: BUG?"

Change-Id: Ibb86b51073b980eda9ecce2cf0b8dd33f058adbf
Merge "Spellchecked /includes directory"