t9117: use --prefix "" instead of --prefix=""

Versions of Perl's Getopt::Long module before 2.37 do not contain
this fix that first appeared in Getopt::Long version 2.37:

* Bugfix: With gnu_compat, --foo= will no longer trigger "Option
  requires an argument" but return the empty string.

Instead of using --prefix="" use --prefix "" when testing an
explictly empty prefix string in order to work with older versions
of Perl's Getopt::Long module.

Also add a paragraph on this workaround to the documentation of
git-svn itself.

Signed-off-by: Kyle J. McKay <mackyle@gmail.com>
Acked-by: Johan Herland <johan@herland.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-svn.txt

@@ -91,6 +91,9 @@ COMMANDS
 NOTE: Before Git v2.0, the default prefix was "" (no prefix). This
 meant that SVN-tracking refs were put at "refs/remotes/*", which is
 incompatible with how Git's own remote-tracking refs are organized.
+If you still want the old default, you can get it by passing
+`--prefix ""` on the command line (`--prefix=""` may not work if
+your Perl's Getopt::Long is < v2.37).
 
 --ignore-paths=<regex>;;
 	When passed to 'init' or 'clone' this regular expression will

t/t9117-git-svn-init-clone.sh

@@ -101,18 +101,18 @@ test_expect_success 'clone with -s/-T/-b/-t assumes --prefix=origin/' '
 	rm -f warning
 	'
 
-test_expect_success 'init with -s/-T/-b/-t and --prefix="" still works' '
+test_expect_success 'init with -s/-T/-b/-t and --prefix "" still works' '
 	test ! -d project &&
-	git svn init -s "$svnrepo"/project project --prefix="" 2>warning &&
+	git svn init -s "$svnrepo"/project project --prefix "" 2>warning &&
 	test_must_fail grep -q prefix warning &&
 	test_svn_configured_prefix "" &&
 	rm -rf project &&
 	rm -f warning
 	'
 
-test_expect_success 'clone with -s/-T/-b/-t and --prefix="" still works' '
+test_expect_success 'clone with -s/-T/-b/-t and --prefix "" still works' '
 	test ! -d project &&
-	git svn clone -s "$svnrepo"/project --prefix="" 2>warning &&
+	git svn clone -s "$svnrepo"/project --prefix "" 2>warning &&
 	test_must_fail grep -q prefix warning &&
 	test_svn_configured_prefix "" &&
 	rm -rf project &&