return 0 if the package is already installed
genpkg now work the same as bulk and testport
No more bulk snapshot to remove
Introduce new AGRESSIVE_DEP_TRACK option
Add a zsh completion file.

  * This is preliminary work, needs to be reviewed by bapt & others.
install zsh completion if zsh is on the system
Fix completion of -d and -o
No need for custom pkgdbdir
Speed up things avoiding make missing
Testing existence of AGRESSIVE_DEP_TRACK is enough no check to check the value
If already package no need to zfs rollback this speeds up things
exclude /var/run/ld-elf.so.hints from the list of the diff
Factorise depends listing and fix it
Simplify things a bit, and still more speed
Exacly match the port name to not avoid some dependencies
introduce sanity_check_pkg

This function check for the available packages and delete the one that with bad
dependency (ie a dependency that has been deleted)

Now when deleting a package because a new version is available, sanity_check is
always run which mean that the package set remains consistent
Do not run sanity check if not necessary
remove dependencies on partial ports
works better if the jails is rolledback during bulks
fix misusage of injail