Warn when loading Mantis Imperative mods with FWE.

Per the mod pages on Nexus:
> FWE: Untested. No issues expected with Mantis.esp and Jello.esp.
> *HOWEVER*, make sure to disable any "tougher stealth" or similar
> components, as it can make one section of this mod quite difficult, if
> not impossible.
>
>   *  It is recommended that you DO NOT load Combat.esp, XP.esp,
> Skillbooks.esp, or Medical.esp in conjunction with FWE, as their
> alterations will conflict with each other and may cause issues.
http://www.nexusmods.com/fallout3/mods/12296