Fixed issue #2218: Tortoise Git Extra Backslash with SUBST Drive Paths

Introduce CGit::CombinePath() to refactor code

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>
Fix spaces to tab

Signed-off-by: Sven Strickroth <email@cs-ware.de>
Check for empty string after mangling and trimming

Signed-off-by: Sven Strickroth <email@cs-ware.de>
Use mangled string for getting icon and storing in history list

Signed-off-by: Sven Strickroth <email@cs-ware.de>
Make CString parameter const

Signed-off-by: Sven Strickroth <email@cs-ware.de>
Fixed issue #1951: Slow switch/checkout dialog

Inspired by code provided by Yue Lin Ho.

Signed-off-by: Sven Strickroth <email@cs-ware.de>