Merge branch 'jk/diff-algo-finishing-touches' into maint

"git diff --diff-algorithm=algo" was understood by the command line
parser, but "git diff --diff-algorithm algo" was not.

* jk/diff-algo-finishing-touches:
  diff: allow unstuck arguments with --diff-algorithm
  git-merge(1): document diff-algorithm option to merge-recursive

Documentation/merge-strategies.txt

@@ -48,6 +48,12 @@ patience;;
 	this when the branches to be merged have diverged wildly.
 	See also linkgit:git-diff[1] `--patience`.
 
+diff-algorithm=[patience|minimal|histogram|myers];;
+	Tells 'merge-recursive' to use a different diff algorithm, which
+	can help avoid mismerges that occur due to unimportant matching
+	lines (such as braces from distinct functions).  See also
+	linkgit:git-diff[1] `--diff-algorithm`.
+
 ignore-space-change;;
 ignore-all-space;;
 ignore-space-at-eol;;

diff.c

@@ -3596,8 +3596,8 @@ int diff_opt_parse(struct diff_options *options, const char **av, int ac)
 		options->xdl_opts = DIFF_WITH_ALG(options, PATIENCE_DIFF);
 	else if (!strcmp(arg, "--histogram"))
 		options->xdl_opts = DIFF_WITH_ALG(options, HISTOGRAM_DIFF);
-	else if (!prefixcmp(arg, "--diff-algorithm=")) {
-		long value = parse_algorithm_value(arg+17);
+	else if ((argcount = parse_long_opt("diff-algorithm", av, &optarg))) {
+		long value = parse_algorithm_value(optarg);
 		if (value < 0)
 			return error("option diff-algorithm accepts \"myers\", "
 				     "\"minimal\", \"patience\" and \"histogram\"");
@@ -3605,6 +3605,7 @@ int diff_opt_parse(struct diff_options *options, const char **av, int ac)
 		DIFF_XDL_CLR(options, NEED_MINIMAL);
 		options->xdl_opts &= ~XDF_DIFF_ALGORITHM_MASK;
 		options->xdl_opts |= value;
+		return argcount;
 	}
 
 	/* flags options */