Store the index for the allowedSlots vector instead of the absolute slot index. This will more gracefully handle edge cases like the available slots for an item having changed when loading the game, or the "allows stacking" property having changed. However the main reason this was done is to ease work on the essimporter.
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.
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.