Code tidiness updates for clang LLVM 5.1 on OS X 10.9.

This commit bundles a number of mostly minor revisions to the code
to deal with deprecations and compiler warnings which arise starting
with the LLVM 5.1 clang compiler on OS X 10.9.

Mostly these are simply removing unused variables.  There are a few
rewrites of casts in Pelican; as Pelican is so old and dubiously
written in the first place, there is no reason to believe this makes
Pelican any less reliable than it already is.
Allowing wxWidgets 2.8.12 again to make life easier for linux users using apt.
Merge branch 'maint13' to pull in updates for compilation on the latest
clang on OS X.