Merge branch 'mm/pull-upload-pack' into maint

"git pull" in recent releases of Git has a regression in the code
that allows custom path to the --upload-pack=<program>.  This has
been corrected.

Note that this is irrelevant for 'master' with "git pull" rewritten
in C.

* mm/pull-upload-pack:
pull: pass upload_pack only when it was given
pull.sh: quote $upload_pack when passing it to git-fetch