Replace svnversion with the short hash

We're no longer using Subversion; the stage1 installer should
be versioned using the git hash.  We use HEAD since if you're
running "make install", it will operate on HEAD.

Also, there is no longer a need to exclude .svn when
creating the tarball
Support PXE installs of Trusty

Initial checkin of PXE support for Trusty.  Configuration
is mostly identical to Raring and Precise, except that we
no longer need to exclude .svn from tarballs.