Fix tests breaking when checkout path contains shell metacharacters

This fixes the remainder of the issues where the test script itself is at
fault for failing when the git checkout path contains whitespace or other
shell metacharacters.

The majority of git svn tests used the idiom

  test_expect_success "title" "test script using $svnrepo"

These were changed to have the test script in single-quotes:

  test_expect_success "title" 'test script using "$svnrepo"'

which unfortunately makes the patch appear larger than it really is.

One consequence of this change is that in the verbose test output the
value of $svnrepo (and in some cases other variables, too) is no
longer expanded, i.e. previously we saw

  * expecting success:
	test script using /path/to/git/t/trash/svnrepo

but now it is:

  * expecting success:
	test script using "$svnrepo"

Signed-off-by: Bryan Donlan <bdonlan@fushizen.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t5700-clone-reference.sh

@@ -51,7 +51,7 @@ diff expected current'
 cd "$base_dir"
 
 test_expect_success 'cloning with reference (no -l -s)' \
-'git clone --reference B file://`pwd`/A D'
+'git clone --reference B "file://$(pwd)/A" D'
 
 cd "$base_dir"