Fixed issue #1992: Compare selected refs fails if tag object is selected

Signed-off-by: Sven Strickroth <email@cs-ware.de>
Extend IsStash check to include both stash commits

Signed-off-by: Sven Strickroth <email@cs-ware.de>
Fixed issue #1991: Disable (by default) certain operations with stash commits

Signed-off-by: Sven Strickroth <email@cs-ware.de>
Treat stash commits correctly when First Parent or Compressed View is enabled

This improves commit 9cf7c959f49f1b4f418815dee8a09bffd27485c9

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>