Mod checker should always check for other TM:PE

[originalfoo]

Currently, if user turns off mod checker, it won't check for other TM:PE

That can cause the save/load issues we are all familiar with.

I'll update it to always check for TM:PE, but only check other mods (incompatible_mods.txt) if the user has enabled checks on startup.

[kvakvs]

I suggest that TM:PE should shut down if other TM:PEs are detected, and either the most stable would remain running, or all of them shut down.

[originalfoo]

If there are more than one TM:PE, regardless of whether enabled or not, it will still cause problems. See #211, particularly Dymanoid's comments.