treewide: correct several "up-to-date" to "up to date"

Follow the Oxford style, which says to use "up-to-date" before the noun,
but "up to date" after it. Don't change plumbing (specifically
send-pack.c, but transport.c (git push) also has the same string).

This was produced by grepping for "up-to-date" and "up to date". It
turned out we only had to edit in one direction, removing the hyphens.

Fix a typo in Documentation/git-diff-index.txt while we're there.

Reported-by: Jeffrey Manian <[email protected]>
Reported-by: STEVEN WHITE <[email protected]>
Signed-off-by: Martin Ågren <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>
Signed-off-by: Pratyush Yadav <[email protected]>

Author: Martin Ågren

po/README

@@ -165,7 +165,7 @@ to contribute an update.  This may be because you would want to improve
 the translation of existing messages, or because the git-gui software
 itself was updated and there are new messages that need translation.
 
-In any case, make sure you are up-to-date before starting your work:
+In any case, make sure you are up to date before starting your work:
 
 	$ git checkout master
 	$ git pull