[Core/Realmd] Fix crash when database version doesn't match.

The general gut feeling is that the Runnable shouldn't ref-count itself, but rather eg.
ACE_Strong_Bound_Ptr should be used for that purpose to ensure deletion at the correct
time. Comments?

Also remove #define MANGOS as that's defined on the command line when building
[Core] Revert part of last commit
Merge pull request #205 from lfxgroove/crash-on-wrong-db-version

[Core/Realmd] Fix crash when database version doesn't match.