Reimplement 'git pull' in C.
* pt/pull-builtin:
pull: remove redirection to git-pull.sh
pull --rebase: error on no merge candidate cases
pull --rebase: exit early when the working directory is dirty
pull: configure --rebase via branch.<name>.rebase or pull.rebase
pull: teach git pull about --rebase
pull: set reflog message
pull: implement pulling into an unborn branch
pull: fast-forward working tree if head is updated
pull: check if in unresolved merge state
pull: support pull.ff config
pull: error on no merge candidates
pull: pass git-fetch's options to git-fetch
pull: pass git-merge's options to git-merge
pull: pass verbosity, --progress flags to fetch and merge
pull: implement fetch + merge
pull: implement skeletal builtin pull
argv-array: implement argv_array_pushv()
parse-options-cb: implement parse_opt_passthru_argv()
parse-options-cb: implement parse_opt_passthru()
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