Have Post::File use shiny new session.fs.file.mv

Also adds a quick and dirty test. Verified working on Linux shell, Linux
meterpreter, and Windows x86 and x64 meterpreter.
Merge branch 'bug/rm7288-post-rename' of github.com:jlee-r7/metasploit-framework into jlee-r7-bug/rm7288-post-rename