- added option to set a sector's tag via compatibility.txt (needed by GZDoom)
- missed a line.
- Fixed: InInventory didn't work quite right with multiple items.
- Added IfHealth based on Blue Shadow's patch.
-fixed the file validity checks in MapData::GetChecksum.

They need to be done per lump, because MapData::Seek can alter the FileReader being used for a specific lump. Even worse, the FileReader will be NULL when the function as it was is called for a map inside a Zip-file.
Merge branch 'master' of https://github.com/rheit/zdoom