Fixes for warnings when building with MSVC

Most warnings are innocuous (wrong type-specifier for forward
declarations, conversion of literals into unsigned integers, warnings
about methods optimized out), but I believe actual bugs were revealed in
vartypedelegate.cpp and combat.cpp.
Revert "Fixes for warnings when building with MSVC"

This reverts commit 46eb20b98ce990756ad1f9af5054f0a571dca43c.
Fixes for MSVC warnings, less overall changes

Kept some fixes from the first round of review. Found out that several
targets weren't being built with the same basic warnings disabled.
Disabled a few warnings for external libraries specifically, rather than
applying them to all targets.
Merge remote-tracking branch 'slothlife/msvc_warning_cleanup'

Conflicts:
	apps/openmw/mwrender/localmap.cpp