[SCM-859] Subversion commands don't work if path or URL contains '@'

There are some oddities where @ escaping is necessary or whether the
path can have a peg revision or not. A discussion on this has been
raised: http://mail-archives.apache.org/mod_mbox/subversion-users/201809.mbox/%3C5f96ccf9-fe6a-8291-4c5a-c90f8e1c70bc%40apache.org%3E

We might need to revise the code after some time when the issues have
been resolved by the Subversion team.

This closes #58
18 files changed