Typo fix.
Fix a warning by adding a missing prototype (and related includes).
Remove a duplicate prototype.

The commit 937ef52 added a prototype for is_feature to viewmap.h, but
there was already a prototype in view.h.  Remove the old one, since
viewmap.h is shorter, and furthermore remove a now-unnecessary #include
of view.h.
Avoid a few trival wrapper functions, and declare some more.

Add an inventory sorting template that takes a pointer-to-method, as
well as a reversed version.  Use these to eliminate a number of trivial
sort_item_* wrappers.

Add dummy declarations for the rest to avoid -Wmissing-declarations
warnings.
Add a few #includes to avoid missing-declaration warnings.
Make some functions static.
Fix a rare crash with door seals expiring
Remove Jesters.

Remove Jesters.
Make pies stop spawning.
Fun is bad.
Specify C++ when testing for warning flags.

Because -E - doesn't know it's C++, and old gcc supported
-Wmissing-declarations in C but not C++.