Merge branch 'maint'

* maint:
git-compat-util.h: use apparently more common __sgi macro to detect SGI IRIX
Documentation: A...B shortcut for checkout and rebase
Documentation/pretty-{formats,options}: better reference for "format:<string>"

diff --cc Documentation/git-checkout.txt
Simple merge

diff --cc Documentation/pretty-formats.txt
Simple merge

diff --cc git-compat-util.h
Simple merge