Fixed gs_do_switch for custom tunnel schemes

I've been getting this bug recently:

```bash
$ g svn fetch
Found possible branch point: svn+xyz://.../trunk => svn+xyz://.../branches/etc, 24743
Found branch parent: (refs/remotes/svn/xap6_ade_reg_split) dd98917ae2e94e414a2a70cf7dfb032aadf89d43
Following parent with do_switch
Malformed network data: Malformed network data at /usr/lib/perl5/site_perl/Git/SVN/Ra.pm line 307
```

This is caused by the custom tunnel protocol, and is rectified by changing the regex for `svn+ssh` to cover all protocols of the form `svn+...`