Setup Vagrant to build Linux packages on CentOS 5.

The goal is to use old glibc so that it can reach more audience (in
particular, RHEL and CentOS users).

Also, we don't compress the executable (using UPX) so that it can be
inspected with ldd. Bonus: no more decompression overhead, faster
startup.

http://code.google.com/p/phantomjs/issues/detail?id=963
Get really ready for 1.8.1.

http://code.google.com/p/phantomjs/issues/detail?id=863