t1402: test forbidden characters in refnames

git-check-ref-format(1) documents that a refname cannot contain a
space, tilde, caret, colon, question-mark, asterisk or open-bracket,
and that it cannot be the single character "@".  Of these, only "?"
was tested as a character embedded in an otherwise-valid refname;
"*" was checked only as a lone character or with --refspec-pattern.

Add the remaining forbidden characters in that embedded form, and
check that "@" alone is rejected even with --allow-onelevel -- where
"@" is otherwise a valid refname component, as "refs/@" confirms.

Signed-off-by: Nikolaus Schuetz <nikolauspschuetz@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: nikolauspschuetz

t/t1402-check-ref-format.sh

@@ -51,12 +51,20 @@ invalid_ref '.refs/foo'
 invalid_ref 'refs/heads/foo.'
 invalid_ref 'heads/foo..bar'
 invalid_ref 'heads/foo?bar'
+invalid_ref 'heads/foo~bar'
+invalid_ref 'heads/foo^bar'
+invalid_ref 'heads/foo:bar'
+invalid_ref 'heads/foo*bar'
+invalid_ref 'heads/foo[bar'
+invalid_ref 'heads/foo bar'
 valid_ref 'foo./bar'
 invalid_ref 'heads/foo.lock'
 invalid_ref 'heads///foo.lock'
 invalid_ref 'foo.lock/bar'
 invalid_ref 'foo.lock///bar'
 valid_ref 'heads/foo@bar'
+valid_ref 'refs/@'
+invalid_ref '@' --allow-onelevel
 invalid_ref 'heads/v@{ation'
 invalid_ref 'heads/foo\bar'
 invalid_ref "$(printf 'heads/foo\t')"