Discussed with: bapt

Save the triggers for later execution

pkg triggers will run them

When a remote repo reports multiple time the same package which could
happen in case the same package do exist with multiple extension or hash

Deduplicate the dependency loading chaing to avoir useless warning

capsicum sandbox prevent opening a file if an element in its path is
an absolute symlinks to a directory.

Another benefit is we can now use the pkg.exec within scripts

This documents the changes introduced in
25943330
as requested in issue #1116.

This enables the triggers to run scripts using most of the pkg.*
functions

It it useful to run pkg.exec for example