TeamCity 5.1.1: Bugfix update

Here is a bugfix update to 5.1, 5.1.1 build 13398. It fixes several issues that were introduced in 5.1, contains several minor improvements and bugfixes. Update is recommended to all users.

Most import changes are:
- in 5.1, the relative path to .sln and command line runner executable were resolved based on the working directory and not checkout directory, as it used to be prior to 5.1. If you updated the path for 5.1 to workaround the issue, please change it back after upgrading to 5.1.1.
- while still in experimental status, we include agent-side checkout for git

For the full list, see our issue tracker.