Adds ability to pull in external drivers (in the form of kernel modules) from a external list.
The files in that list (either TCEs or Debian Wheezy packages) are included in the bundle
(and the ISO built using that bundle) in such a way that the kernel modules on the list
are are extracted from those TCEs and the modules themselves are started during the
Microkernel boot process.  This gives us the ability to load drivers for a specific network
adapter (for example) into a customized version of the Microkernel during the bundle build
process simply by having access to the TCE or Debian Wheezy package containing the
drivers for that network adapter.
adding in support for specification of file containing a list of additional (local) extensions to install during the boot process
Handle case where user does not enter the two new options (both of which are truly optional)
Merge pull request #12 from tjmcs/tb/build-nextgen-mk

Tb/build nextgen mk