Spin off hivex as a separate upstream project.

Spin off hivex as a separate upstream project.

This commit makes the semi-independent hivex library into a
separate upstream project.  The git repo for hivex is now:

http://git.annexia.org/?p=hivex.git;a=summary

Downloads of hivex are available here:

http://libguestfs.org/download/

All questions, patches, bugs etc should be sent to the libguestfs
mailing list and bug tracker.