EDIT_GETLIN vs monpolycontrol

EDIT_GETLIN vs monpolycontrol

For wizard mode 'monpolycontrol', the getlin() answer buffer for the
"Change <monster> @ <x,y> into what kind of monster?" prompt is also
used to format the coordinate portion of that prompt, so when
EDIT_GETLIN is enabled getlin() was inadvertently given "<x,y>" to use
as default response.  Clear it after the prompt is formatted instead
of via an initializer.  Also, shorten the prompt on the first try:
"Change <monster> @ <x,y> into what?", expanding to the old prompt if
retry is needed.

This also allows specifying 'chameleon' when <monster> is a chameleon,
'doppelganger' when it's a doppelganger, and 'sandestin' when it's one
of those (but not 'doppelganger' when it's a chameleon or sandestin,
and so forth), instead of blanket refusal to accept any non-vampire
shapechanger as the choice.