[entropy.client.interfaces.dep] use set type for internal selected_matches

Given the current use cases, this is faster.
[entropy.client.interfaces.dep] introduce rewrite_selected_matches fixup code

See Sabayon bug #4475
[matter] improve ACCEPT_KEYWORDS setup basing on the "stable" parameter

This tweak makes possible to directly skip depgraph generation if
the root node (the dependency to check, last node of the toposorted
queue) is already up-to-date (wrt to stable: yes, for example).

This is what Portage does internally (using backupenv) and may break
in future releases without notice. So, keep the settings["ACCEPT_KEYWORDS"]
setup as a guard, to ensure the safety property.
Release Entropy 227
Tagging Entropy version 227
[entropy.tools] add is_author_bday method

The cake is a lie!
[Rigo] add author bday check
[Rigo] add preferences menu to show available kernel binaries (both LTS and not)
[Rigo] update rigo.pot
[kswitch] add virtual/linux-binary-lts variable string
[Rigo] use kswitch to get the kernel binary package names
[kswitch] improve API usability by external components (RigoDaemon)
[kswitch] fix undefined reference "kernel_atom" in PreparedSwitch.post()
[RigoDaemon] implement transparent kernel-switcher support
[RigoDaemon] use KernelSwitcher.list() rather than reimplementing the same logic
Release Entropy 228
Tagging Entropy version 228
[RigoDaemon] do not trigger kernel-switcher if kernel is already installed
[entropy.server] add another QA test, guard against revision downgrades
Merge remote-tracking branch 'upstream/master'