_slot_operator_update_probe: fix bug #508762

This fixes the check_reverse_dependencies function (inside the depgraph
_slot_operator_update_probe method) to account for irrelevant parent
atoms from parents that need to be rebuilt or have been involved in
unsolved slot conflicts.

X-Gentoo-Bug: 508762
X-Gentoo-Bug-URL: https://bugs.gentoo.org/show_bug.cgi?id=508762
Reviewed-by: Brian Dolbec <dolsen@gentoo.org>
QA: Add a set of checks for bash-completion files

Add checks for common mistakes when installing bash completion files:
legacy directory, incorrect naming, missing aliases, deprecated 'have'
function.

Changes in v2:

- silenced output (error) when sourcing completion files,

- faked _have() to enable all conditional completions in the tested
  files.

Changes in v3:

- missing EPREFIX.
Merge branch 'master' into all-in-one
Merge branch 'qa-bashcomp' into all-in-one

Conflicts:
	bin/misc-functions.sh