Update loading of configuration of sets.

- Ignore VCS directories.
- Ignore directories and files whose names start with "." or end with "~".
- Fix "BytesWarning: Comparison between bytes and string", which was occurring
  when any directory in /etc/portage/sets exists.
Sort PORTAGE_ARCHLIST.
Support @profile package set for bug #532224

Add support for a new @profile set which allows the profile to pull
in additional packages that do not belong to the @system set.

The motivation to have @profile separate from @system is that
@system packages may have incomplete dependency specifications
(due to long-standing Gentoo policy), and incomplete dependency
specifications have deleterious effects on the ability of emerge
--jobs to parallelize builds. So, unlike @system, packages added to
@profile do not hurt emerge --jobs parallelization.

Packages are added to the @profile set in the same way that they are
added to the @system set, except that atoms in the @profile set are
not preceded with a '*' character. Also, the @profile package set
is only supported when 'profile-set' is listed in the layout.conf
profile-formats field of the containing repository.

X-Gentoo-Bug: 532224
X-Gentoo-Bug-URL: https://bugs.gentoo.org/show_bug.cgi?id=532224
Acked-by: Alexander Berntsen <bernalex@gentoo.org>
search._xmatch: handle aux_get KeyError (525718)

Since commit 55c8c8bc7a781e3f71ce92922eea64ad4cafce3c, emerge --search
can raise an unhandled KeyError if a pkg_desc_index contains a stale
package. Handle it with the same error message used for other aux_get
failures.

Fixes: 55c8c8bc7a78 ("Add emerge --search-index option.")
X-Gentoo-Bug: 525718
X-Gentoo-Bug-URL: https://bugs.gentoo.org/show_bug.cgi?id=525718
When using --verbose, always print ::repository in list of packages for installation.

--verbose-main-repo-display option is no longer supported.
3 calls to deprecated portage.repository.config.RepoConfigLoader.mainRepo() function
have been deleted.
Blacklist _ variable.
emerge --info: Modernize output of configuration of repositories.

- Always print detailed configuration of repositories.
- Always skip PORTAGE_REPOSITORIES variable.
- Always skip deprecated PORTDIR, PORTDIR_OVERLAY and SYNC variables.
emerge --info: Always print ::repository.

1 call to deprecated portage.repository.config.RepoConfigLoader.mainRepo() function
has been deleted.
emerge --verbose --quiet-repo-display: Delete deprecated code.

Use portage.repository.config.RepoConfigLoader.__iter__() instead of deprecated
PORTDIR and PORTDIR_OVERLAY.
1 call to deprecated portage.repository.config.RepoConfigLoader.mainRepoLocation()
function has been deleted.
_compute_abi_rebuild_info: fix bug #532594

Since commit 3f0799054b4e5ef88feb59d20d262668ca79df33, there has been
a faulty variable assignment inside _compute_abi_rebuild_info which
assigns a bool value to the inst_pkg variable which is intended to
refer to a Package instance. Fix it to assign a correct value.

Fixes: 3f0799054b4e ("_compute_abi_rebuild_info: fix bug #521990")
X-Gentoo-Bug: 532594
X-Gentoo-Bug-URL: https://bugs.gentoo.org/show_bug.cgi?id=532594
portageq pquery: Search ebuilds in all repositories be default.

--all-repos option is no longer supported.
1 call to deprecated portage.repository.config.RepoConfigLoader.mainRepo() function
has been deleted.
portage.dbapi.bintree.binarytree: Delete main-repository-reliant microoptimization in index of binary packages.

This microoptimization cannot work when no main repository exists.
1 call to deprecated portage.repository.config.RepoConfigLoader.mainRepo() function
has been deleted.
portage.tests.dbapi.test_portdb_cache: Delete deprecated code.

9 calls to deprecated portage.repository.config.RepoConfigLoader.mainRepoLocation()
function have been deleted.
portage.tests.glsa.test_security_set: Delete deprecated code.

1 call to deprecated portage.repository.config.RepoConfigLoader.mainRepoLocation()
function has been deleted.
emerge --info: Check metadata/timestamp.chk in all repositories.

1 use of deprecated PORTDIR has been deleted.