tag, branch, for-each-ref: add --ignore-case for sorting and filtering

This options makes sorting ignore case, which is great when you have
branches named bug-12-do-something, Bug-12-do-some-more and
BUG-12-do-what and want to group them together. Sorting externally may
not be an option because we lose coloring and column layout from
git-branch and git-tag.

The same could be said for filtering, but it's probably less important
because you can always go with the ugly pattern [bB][uU][gG]-* if you're
desperate.

You can't have case-sensitive filtering and case-insensitive sorting (or
the other way around) with this though. For branch and tag, that should
be no problem. for-each-ref, as a plumbing, might want finer control.
But we can always add --{filter,sort}-ignore-case when there is a need
for it.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t3203-branch-output.sh

@@ -89,6 +89,11 @@ test_expect_success 'git branch --list -v pattern shows branch summaries' '
 	awk "{print \$NF}" <tmp >actual &&
 	test_cmp expect actual
 '
+test_expect_success 'git branch --ignore-case --list -v pattern shows branch summaries' '
+	git branch --list --ignore-case -v BRANCH* >tmp &&
+	awk "{print \$NF}" <tmp >actual &&
+	test_cmp expect actual
+'
 
 test_expect_success 'git branch -v pattern does not show branch summaries' '
 	test_must_fail git branch -v branch*
@@ -196,4 +201,28 @@ test_expect_success 'local-branch symrefs shortened properly' '
 	test_cmp expect actual
 '
 
+test_expect_success 'sort branches, ignore case' '
+	(
+		git init sort-icase &&
+		cd sort-icase &&
+		test_commit initial &&
+		git branch branch-one &&
+		git branch BRANCH-two &&
+		git branch --list | awk "{print \$NF}" >actual &&
+		cat >expected <<-\EOF &&
+		BRANCH-two
+		branch-one
+		master
+		EOF
+		test_cmp expected actual &&
+		git branch --list -i | awk "{print \$NF}" >actual &&
+		cat >expected <<-\EOF &&
+		branch-one
+		BRANCH-two
+		master
+		EOF
+		test_cmp expected actual
+	)
+'
+
 test_done