git-svn: fix commiting renames over DAV with funky file names

git-svn: fix commiting renames over DAV with funky file names

Renaming files with non-URI friendly characters caused
breakage when committing to DAV repositories (over http(s)).

Even if I try leaving out the $self->{url} from the return value
of url_path(), a partial (without host), unescaped path name
does not work.

Filenames for DAV repos need to be URI-encoded before being
passed to the library.  Since this bug did not affect file://
and svn:// repos, the git-svn test library needed to be expanded
to include support for starting Apache with mod_dav_svn enabled.

This new test is not enabled by default, but can be enabled by
setting SVN_HTTPD_PORT to any available TCP/IP port on
127.0.0.1.

Additionally, for running this test, the following variables
(with defaults shown) can be changed for the suitable system.
The default values are set for Debian systems:

  SVN_HTTPD_MODULE_PATH=/usr/lib/apache2/modules
  SVN_HTTPD_PATH=/usr/sbin/apache2

Signed-off-by: Eric Wong <normalperson@yhbt.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>