fix issue #510, pull request #519 - vomit effects

fix issue #510, pull request #519 - vomit effects

Add some vomiting effects:

Trigger divine wrath if hero vomits at an altar's location.  (What
about adding throne and maybe sink special effects too?)

If poly'd into a yellow dragon, breathe (acid) on self.  (I'm not
sure why.)

If on ice and poly'd into an acidic form, melt the ice.  Also,
change melt_ice() to give its message when melting happens at the
hero's location even if hero can't see.

Fixes #519
Fixes #510