libexec Makefile: Fix negation typo
common.sh.dragonfly: Fix typo
Implement createfs and destroyfs on DragonFly after all

While I could have used the stock destroyfs, the createfs feature
appears to require some knowledge of ZFS.  Since they were already in
common.sh.freebsd, I just created simpler versions in the DragonFly
file.  It appears easier to use these functions than avoid them.
Fix and improve poudriere ports

Several options were removed from ports.sh:
  -F (ZFS option)
  -f (ZFS option)
  -B (SVN option)

The rsync method (really cpdup) was implemented, and the git method was
reimplemented.  The remaining methods were removed.

A timehack was added to the portstree list, which required a modification
to common.sh.  This timestamp reflects the last modification time of the
ports tree, causd by use of -u or -c options.