Merge branch 'mz/reset-misc'

Various 'reset' optimizations and clean-ups, followed by a change
to allow "git reset" to work even on an unborn branch.

* mz/reset-misc:
  reset: update documentation to require only tree-ish with paths
  reset [--mixed]: use diff-based reset whether or not pathspec was given
  reset: allow reset on unborn branch
  reset $sha1 $pathspec: require $sha1 only to be treeish
  reset.c: inline update_index_refresh()
  reset.c: finish entire cmd_reset() whether or not pathspec is given
  reset [--mixed]: only write index file once
  reset.c: move lock, write and commit out of update_index_refresh()
  reset.c: move update_index_refresh() call out of read_from_tree()
  reset.c: replace switch by if-else
  reset: avoid redundant error message
  reset --keep: only write index file once
  reset.c: share call to die_if_unmerged_cache()
  reset.c: extract function for updating {ORIG_,}HEAD
  reset.c: remove unnecessary variable 'i'
  reset.c: extract function for parsing arguments
  reset: don't allow "git reset -- $pathspec" in bare repo
  reset.c: pass pathspec around instead of (prefix, argv) pair
  reset $pathspec: exit with code 0 if successful
  reset $pathspec: no need to discard index

Documentation/git-reset.txt

@@ -8,20 +8,20 @@ git-reset - Reset current HEAD to the specified state
 SYNOPSIS
 --------
 [verse]
-'git reset' [-q] [<commit>] [--] <paths>...
-'git reset' (--patch | -p) [<commit>] [--] [<paths>...]
+'git reset' [-q] [<tree-ish>] [--] <paths>...
+'git reset' (--patch | -p) [<tree-sh>] [--] [<paths>...]
 'git reset' [--soft | --mixed | --hard | --merge | --keep] [-q] [<commit>]
 
 DESCRIPTION
 -----------
-In the first and second form, copy entries from <commit> to the index.
+In the first and second form, copy entries from <tree-ish> to the index.
 In the third form, set the current branch head (HEAD) to <commit>, optionally
-modifying index and working tree to match.  The <commit> defaults to HEAD
-in all forms.
+modifying index and working tree to match.  The <tree-ish>/<commit> defaults
+to HEAD in all forms.
 
-'git reset' [-q] [<commit>] [--] <paths>...::
+'git reset' [-q] [<tree-ish>] [--] <paths>...::
 	This form resets the index entries for all <paths> to their
-	state at <commit>.  (It does not affect the working tree, nor
+	state at <tree-ish>.  (It does not affect the working tree, nor
 	the current branch.)
 +
 This means that `git reset <paths>` is the opposite of `git add
@@ -34,9 +34,9 @@ Alternatively, using linkgit:git-checkout[1] and specifying a commit, you
 can copy the contents of a path out of a commit to the index and to the
 working tree in one go.
 
-'git reset' (--patch | -p) [<commit>] [--] [<paths>...]::
+'git reset' (--patch | -p) [<tree-ish>] [--] [<paths>...]::
 	Interactively select hunks in the difference between the index
-	and <commit> (defaults to HEAD).  The chosen hunks are applied
+	and <tree-ish> (defaults to HEAD).  The chosen hunks are applied
 	in reverse to the index.
 +
 This means that `git reset -p` is the opposite of `git add -p`, i.e.