fix messaging in obstructed() in lock.c

fix messaging in obstructed() in lock.c

From ais523's recent list of bugs:
If a long worm tail is blocking the door, and you're blind and not
telepathic, attempting to close the door marks the position of its head.

From an email received in late September 2014 before the git conversion:
> I was trying to close a door, not noticing that there was a garter
> snake there, and this message resulted:
> The garter snake stands in the way!
> I haven't tried it with any other monsters without feet, but
> "stands in the way" appears to be the wrong way to describe
> this situation...

Both of the above were found in the same function in lock.c