cave: fix knight's move crash in update_view_one

Signed-off-by: Elly Fong-Jones <elly@leptoquark.net>
Merge pull request #232 from elly/vinfo-crash

cave: fix knight's move crash in update_view_one
Fix problem where the game would abort if you didn't already have a savefile directory on Unices.
Fix check for MIN_SHROOM
Merge pull request #233 from NickMcConnell/minshroom

Fix check for MIN_SHROOM that made Mushrooms of Second Sight look weird
Add tiles for new food items.  Thanks to PowerWyrm.  Closes #1741.