svn test: escape peg revision separator using empty peg rev

svn test: escape peg revision separator using empty peg rev

This test script uses "svn cp" to create a branch with an @-sign in
its name:

	svn cp "pr ject/trunk" "pr ject/branches/not-a@{0}reflog"

That sets up for later tests that fetch the branch and check that git
svn mangles the refname appropriately.

Unfortunately, modern svn versions interpret path arguments with an
@-sign as an example of path@revision syntax (which pegs a path to a
particular revision) and truncate the path or error out with message
"svn: E205000: Syntax error parsing peg revision '{0}reflog'".

When using subversion 1.6.x, escaping the @ sign as %40 avoids trouble
(see 08fd28bb, 2010-07-08).  Newer versions are stricter:

	$ svn cp "$repo/pr ject/trunk" "$repo/pr ject/branches/not-a%40{reflog}"
	svn: E205000: Syntax error parsing peg revision '%7B0%7Dreflog'

The recommended method for escaping a literal @ sign in a path passed
to subversion is to add an empty peg revision at the end of the path
("branches/not-a@{0}reflog@").  Do that.

Pre-1.6.12 versions of Subversion probably treat the trailing @ as
another literal @-sign (svn issue 3651).  Luckily ever since
v1.8.0-rc0~155^2~7 (t9118: workaround inconsistency between SVN
versions, 2012-07-28) the test can survive that.

Tested with Debian Subversion 1.6.12dfsg-6 and 1.7.5-1 and r1395837
of Subversion trunk (1.8.x).

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Tested-by: Michael J Gruber <git@drmicha.warpmail.net>
Signed-off-by: Eric Wong <normalperson@yhbt.net>