TortoiseGitMerge: Update CBaseView related to space/tab

Line was not indented properly when pressing tab key with text selection

Check all lines when saving to prevent false reporting whitespace problem

When loading file, detecting first 10000 lines may be OK

Based on TortoiseSVN revision 24355, 24356, 24357

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