git-gui: Revert "Don't modify CREDITS-FILE if it hasn't changed." This reverts commit 92446aba47b0e0db28f7b858ea387efcca30ab44. Too many users have complained about the credits generator in git-gui, so I'm backing the entire thing out. Signed-off-by: Shawn O. Pearce <spearce@spearce.org>