Allow MapAddress .exit even if AllowDotExit is 0

If AllowDotExit is 0 (the default) MapAddress doesn't permit a .exit address to be set as the destination. It is desirable to keep AllowDotExit disabled for security reasons, but there shouldn't be any harm in always permitting MapAddress entries because the user must enter these manually. This feature is desirable because it allows the user to force exit enclaving.

Using Tor v0.2.2.32 (git-877e1774).