fix apt list output for pkgs in dpkg ^rc state

Packages in the "deinstall ok config-file" have no candidate or
instaleld version. So they must be special cased in the apt list
generation.
Notice the user about "apt list -a" when only a single hit if found

If the user is using "apt list pattern" and there is only a single
hit, notice about "--all-versions" as this is what the user may
be interessted in
Fix insecure file permissions when using FileFd with OpenMode::Atomic

Commit 7335eebea6dd43581d4650a8818b06383ab89901 introduced a bug
that caused FileFd to create insecure permissions when FileFd::Atomic
is used. This commit fixes the permissions and adds a test.

The bug is most likely caused by the confusing "Perm" parameter
that is passed to Open() - its not the file permissions but intead
the "mode" part of open/creat.
Rename FileFd::Open() Perms to AccessMode

Bug lp:#1304657 was caused by confusion around the name Perms.
The new name AccessMode should make it clear that its not the
literal file permissions but instead the AccessMode passed to
open() (i.e. the umask needs to be applied)
improve umask/fchmod code readability
Merge remote-tracking branch 'mvo/bugfix/apt-search-case' into debian/sid
Merge remote-tracking branch 'mvo/bugfix/lp1304657-perms' into debian/sid
apt: Minor typo in 'apt' man page (closes: #743657)
prepare 1.0.1 release
fix test-failure in adt
use wildcard to get files in our library makefiles

The explicit listing is a pain every time you want to add a file to the
list and serves no propose as we list all files there anyway, so this is
not only easier but also documents this fact.

Git-Dch: Ignore
be able to run abicheck from any directory

Git-Dch: Ignore
do not create an (additional) empty compressor

FileFd code knows how to deal with such a compressor, so it isn't a
problem, but it is absolutely not needed as we already have an
(matching) identity compressor with '.' earlier in the list.

Git-Dch: Ignore
don't double-count seeks in FileFd::Skip for bzip/xz

FileFd::Read already deals with the increase of the skipposition so that
we as the caller in FileFd::Skip really shouldn't increase it, too.
deal with umask only if we really need to for mkstemp

As the comment actually says: open() does the umask dance by itself, so
we don't need to do it for it. We have to do it after mkstemp in Atomic
though, so move it into the if.

Also removes the "micro-optimisation" "FilePermissions == 600" as it
doesn't trigger at the moment anyway as 600 != 0600.
extend FileFd test behond basic permission tests

We now do Open, Write and Read (the later multiple ways) for each
permission and each compressor we have configured to cover more cases
and especially ensure that compressors do not change our premissions.

This test is also to be credited for discovering the skippos-fix.

Git-Dch: Ignore
consider priorities only for downloadable pkgs in resolver

A package which can't be downloaded anymore is very likely dropped from
a release and can therefore no longer be 'standard' (or similar). We
therefore do not grant points for them anymore and demote them to
prio:extra instead which helps other packages breaking them away even if
they have a lower priority.

The testcase was initially created by Michael Vogt and just amended.
Merge remote-tracking branch 'mvo/bugfix/apt-list-rc-pkgs' into debian/sid
Merge remote-tracking branch 'mvo/feature/helpful-apt-list' into debian/sid

Conflicts:
	test/integration/test-apt-cli-list
Merge remote-tracking branch 'upstream/debian/sid' into bugfix/lp13086670