Fixed|All Games: Read-only cvar "game-save-last-slot" incorrect

The last-used slot number should be determined from the slot id.
libcore|FS: Added more log entries about file pruning
Fixed|Windows|MSVC: Build and deployment with Qt 5 and VS 2013
Fixed|libcore|libcommon: File already exists when trying to save game

Two issues were fixed:

- ArchiveFeed would abort a repopulation prematurely due to a
  "return" in place of "continue".

- ArchiveEntryFile wasn't making sure that the File's modification
  timestamp matched the archive entry timestamp. This lead to an
  unnecessary prune (but the file wasn't recreated due to the above
  issue).

Also removed an unnecessary populate() call in libcommon's GameSession.

IssueID #1802
Merge remote-tracking branch 'remotes/origin/master' into revise-map-geometry-generation