Mimikatz extension

I've not seen a pull request for the sessiondump extension so I had a play with mimikatz to convert it into an extension. I have created the pull request to get some discussion going and some feedback as my C-fu is weak. I also believe mimikatz is a far better name than sessiondump :)

Framework code is here: https://github.com/rapid7/metasploit-framework/pull/1747

Main issues:
* License - The majority of Mimikatz is Creative Commons Non Commercial (some parts are just Creative Commons). I think this is compatible with MSF but not sure how it sits with Rapid7's commercial offerings (does it need to be excluded from pro etc?). I guess changes to the LICENSE will be required and I have left the license intact in the source.

* Mimikatz functions tend not to return useful values, but dump everything to wcout. I have redirected the buffer to my own stringbuffer (thanks http://clymb3r.wordpress.com/2013/04/09/modifying-mimikatz-to-be-loaded-using-invoke-reflectivedllinjection-ps1/) and modified some of the output format to retrieve CSV style responses. CSV format may not be the best way to format this as passwords may contain " , etc?

* Mimikatz is compiled with Unicode strings, lots of testing will probably be required to ensure Unicode characters aren't lost when returned to the user especially the handling of this encoding on the framework side.

* Mimikatz defines the std namespace. This has a small clash with ReflectiveDLLInjection which uses Hash(). Renamed to _Hash()

* Some Mimikatz structures clash with ReflectiveDLLInjection structures. I have prepended ___ to them to mostly avoid this.

* I have left in all functionality and custom commands can be used to access most if not all functions!<del>* I have probably included far more code than is required for the functions people will be interested in, some can probably be stripped away.</del>

<del>So far I have wdigest working (the other authentication storages should be relatively straightforward to add as new functions now).</del>

<del>Currently the user cannot run the command twice, without crashing meterpreter, I have to work out how to cleanup or leave it in a nice state between commands.</del>

<del>I also need to work out how to get it to compile in Debug and I have not tested (or compiled) x64...</del>
<del>I could use a volunteer to compile and test in x64? :)</del>

Tested x86 Win7, x64 Win8.