git: Improve detection of local changes.
libgpg-error currently fails to update with kdesrc-build, ultimately due to git-rebase complaining that there are local changes that need to be stashed or reverted first. These local changes are inherent to the libgpg-error build process, but even so, kdesrc-build *does* check for local changes and stashes them automatically. But it turns out the current check from git of whether there are local changes (using git-diff) gives a 'no changes' answer with libgpg-error's modifications. So git-diff thinks there's no change, but git-rebase thinks there is a change. git-status --short gives an answer matching git-rebase, so switch to that instead. git-status also gives answers for both the index and the working tree at the same time to the updated code is even a bit shorter now.