Add Ubuntu package script
Add Ubuntu build instructions
Check for expected test environment

This is in response to the Ubuntu-inspired Bash issue:
<https://github.com/ajnelson/regxml_extractor/issues/5>
Update hivex's gnulib reference

A compilation error was cropping up with 'gets' not being
found.
Add Fedora 18 build scripts
Apply Hivex build fix from Hilko

Found necessary for CentOS.
Add CentOS 6.4 test