Don't use "selfmade" base64 encoding class

Signed-off-by: Sven Strickroth <email@cs-ware.de>
Fix warnings for possible null dereferences

Programmatically assumeValid and skipWorktree are always set if callback is set.

Signed-off-by: Sven Strickroth <email@cs-ware.de>
Reduce calls to callback

Do as documented: Only call "callback" if skipWorktree or assumeValid is set to true.

Signed-off-by: Sven Strickroth <email@cs-ware.de>
Fixed issue #1896: Switch/Checkout Branch name resets itself after browsing for a branch

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