PowerShell post module download and exec

This adds sempervictus's PowerShell post module, along with a default
post module one can use for quick testing (for expected results, see
the screencap Gist at https://gist.github.com/6011cb87b01e970deca8

[Closes #403]

Squashed commit of the following:

commit c6b5a6aac1dc8781c67b611289d7710129592e83
Author: Tod Beardsley <todb@metasploit.com>
Date:   Mon May 21 14:43:48 2012 -0500

    Minor tweaks to language

commit ef088e135cd7b0ccb514a3011889154661d5bd09
Merge: 0a05455 1e14211
Author: Tod Beardsley <todb@metasploit.com>
Date:   Mon May 21 14:34:27 2012 -0500

    Merge remote branch 'todb/default-powershell' into Pull403

commit 0a0545558604c53d4648e3314ca8963ff9b225a7
Author: Tod Beardsley <todb@metasploit.com>
Date:   Mon May 21 14:33:33 2012 -0500

    Reverting unrelated telnet fix

    While I'm sure it's great, it needs to be tested.

commit 1e1421102b44a4c60c6eb9b442227075e959d7c6
Author: Tod Beardsley <todb@metasploit.com>
Date:   Mon May 21 14:14:09 2012 -0500

    Adds a default path to a script for exec_powershell.rb

commit 9978787f44896d06744d50febf4344111edcd7b1
Author: Tod Beardsley <todb@metasploit.com>
Date:   Mon May 21 14:06:46 2012 -0500

    Adds a new default powershell script

commit 25b605949fbf772e95a510162ca5af510c59788f
Author: RageLtMan <rageltman [at] sempervictus>
Date:   Mon May 21 14:15:15 2012 -0400

    Synchronized SVIT version of lib...powershell.rb to github. Adds timeout option, check for script encoding, etc. Added post/windows/manage/powershell folder with script execution module. Other modules which can be placed here would be WinRM meterp exec, PS persistence, etc

commit c4a7fd932fb8850de732bfa911cf8d729a5db42d
Merge: 21b31f1 36207eb
Author: RageLtMan <rageltman [at] sempervictus>
Date:   Mon May 21 14:07:26 2012 -0400

    msfvenom formatting merge conflict fix

commit 36207eb21ee04483c19790b5db7855d0a715e43d
Merge: c77eb03 4772c12
Author: RageLtMan <rageltman [at] sempervictus>
Date:   Mon May 21 14:06:07 2012 -0400

    Merge branch 'master' of https://github.com/rapid7/metasploit-framework

commit 21b31f10c505862c14234824d4dabbb6fdfe7cbb
Merge: 81a7d62 c77eb03
Author: RageLtMan <rageltman [at] sempervictus>
Date:   Fri May 18 12:57:52 2012 -0400

    Merge branch 'master' into powershell

commit c77eb03ca4428a741f5d231b3ec1cf80c90e9395
Merge: 89d5af7 52183aa
Author: RageLtMan <rageltman [at] sempervictus>
Date:   Fri May 18 12:57:21 2012 -0400

    Merge branch 'master' of https://github.com/rapid7/metasploit-framework

commit 89d5af7ab2fe1ce31cd70561893d94bb73f3762c
Author: RageLtMan <rageltman [at] sempervictus>
Date:   Fri Mar 2 01:28:02 2012 -0500

    Banner encoding fix when running against dd-wrt on ruby 1.9.3

commit 81a7d62c6dab8404c1c0566a8be84c7280edeef8
Author: RageLtMan <rageltman [at] sempervictus>
Date:   Tue Mar 20 20:19:13 2012 -0400

    powershell for msfvenom

commit 672c7bc37ea37a3b111f755ef17fe0c16047e488
Merge: 3e86dc4 ed542e2
Author: RageLtMan <rageltman [at] sempervictus>
Date:   Tue Mar 20 20:08:12 2012 -0400

    exe.rb merge cleanup

commit 3e86dc4c40da1df3d0ff4a9ab6fffe8eeda52544
Author: RageLtMan <rageltman [at] sempervictus>
Date:   Tue Mar 20 20:06:03 2012 -0400

    psh encoder cleanup

commit f619ed477fef7a2830b99ce6a9b27bb523c9d3ce
Author: RageLtMan <rageltman@sempervictus.com>
Date:   Sun Feb 5 13:35:11 2012 -0500

    method call fix for psh-net encoder

commit 7b035e6da0ead328aebbfdf9fbbebed506cdca18
Author: RageLtMan <rageltman@sempervictus.com>
Date:   Fri Feb 3 18:53:54 2012 -0500

    PS encoders: .net and architecture dependent native (psh-net, psh)

commit 7a2749bf2682686a87d37d240e61adece53fba8e
Merge: 32730b9 f89853d
Author: RageLtMan <rageltman@sempervictus.com>
Date:   Fri Feb 3 18:38:03 2012 -0500

    Merge branch 'master' into powershell

commit 32730b96be4c9bd73f1f45b5d2d4330b8fb72cb8
Merge: e69fcd1 f6a6963
Author: RageLtMan <rageltman@sempervictus.com>
Date:   Wed Jan 25 10:33:17 2012 -0500

    Merge branch 'master' of https://github.com/rapid7/metasploit-framework into powershell

commit e69fcd1a83412d6c0c96605b5acf0675e5b07205
Author: RageLtMan <rageltman@sempervictus.com>
Date:   Wed Jan 25 07:59:38 2012 -0500

    msfvenom psh addition

commit 9a5d8ead7e69c40ff5e9a73244165a5685ca47ec
Author: RageLtMan <rageltman@sempervictus.com>
Date:   Wed Jan 25 07:29:38 2012 -0500

    Proper author reference

commit 9fd8ac75a89ca2678b0d09192227eb23f00bf549
Author: RageLtMan <rageltman@sempervictus.com>
Date:   Tue Jan 24 19:07:30 2012 -0500

    Fix script handling

commit fa363dfe965382a9f89ff404398e38e8f164c11a
Author: RageLtMan <rageltman@sempervictus.com>
Date:   Tue Jan 24 17:31:09 2012 -0500

    added Msf::Post::Windows::Powershell, reworked post module to use mixin

commit e078d15b5464ff47ce616334d8cb1aa84a00df33
Author: RageLtMan <rageltman@sempervictus.com>
Date:   Mon Jan 23 13:42:35 2012 -0500

    vprint_good change

commit 355f8bb19a62d974c5c89079dd26dd4cbb756c0a
Author: RageLtMan <rageltman@sempervictus.com>
Date:   Mon Jan 23 12:50:51 2012 -0500

    exec powershell module

commit 5f9509444953f25352c994f90cae8a168878f7ea
Author: RageLtMan <rageltman@sempervictus.com>
Date:   Mon Jan 23 12:45:41 2012 -0500

    powershell encoder support - Redmine Feature #6049