Support big files: Read stdout asynchronously

Signed-off-by: Sven Strickroth <email@cs-ware.de>
Pipe filters through sh.exe

This is needed as long as TortoiseGit depends on git.exe, because otherwise shell scripts cannot be used as filters (i.e., they are not Win32 applications).

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