CVE-2016-3105: Mercurial vulnerable to arbitrary code execution when converting Git repos

The security patch modifies the init method of the convert_git class in hgext/convert/git.py to explicitly convert paths to absolute paths. This change addresses the core vulnerability where relative paths could be interpreted as Git URL formats (like 'ext::' protocol handlers), enabling command injection. The test cases demonstrate protection against repository names starting with 'ext::' which could execute shell commands. The vulnerable function is the entry point for git repository conversion handling.