Refactor lanattacks ruby code, add command dispatcher

The lanattacks module didn't seem to have a command dispatcher, and
hence loading the module would always result in a failure. This
commit fixes this problem.

The commit contains a bit of a refactor of the lanattacks code to be
a little more modular. It also has a shiny new dispatcher which breaks
the DHCP and TFTP functionality up into separate areas.
Fix comments, indenting and pxexploit module

Updated the comments and indentation so they're not blatantly wrong.

Adjusted the pxexploit module so that it doesn't break any more as
a result of the refactoring.
Remote shebang and fix pxexeploit
Merge branch 'lanattacks_fix' of git://github.com/OJ/metasploit-framework into OJ-lanattacks_fix