- make svn checkout --trust-server-cert option conditional, since
this option is not supported by versions prior to subversion 1.6.

- Trim user prefix from tarball filename.
This enables tar_scm service to be used with git and ssh transport
(in conjuction with a passphrase less ssh-pubkey). Example Git URL:
git@gitrepo.tld:foobar.git

- git 1.6.x and very likely other version only support
"show --pretty=format:%at" as parameter with "format:" prefix.
git show --pretty=%at is also support by recent git versions. (forwarded request 98423 from dgollub)