Better checks for set-default and delete options

Quits with error message if the snapshot name doesn't start with
SNAP_PREFIX, or if it doesn't exist. Imagine the damage one could
do with something like "set-default @home".
Merge from development branch on launchpad

manpages not from launchpad
Better checks on snapshot deleting or changing default

Currently "apt-btrfs-snapshot set-default @home" will succeed.
However "apt-btrfs-snapshot delete @home" would probably fail if
@home were mounted. Still I think that apt-btrfs-snapshot should
only accept its own snapshots.
Apt log file parser classes taking shape
History.log parsing and pretty printing done

It only checks /var/log/apt/history.log so once a month you might
get less info than you should. TODO read history.log.1.gz too if
it exists.
AptHistory classes factored out and tests implemented.
AptHistoryEntry parsing to dict, time limited change listing
Clean-ups and small improvements to AptHistory
noatime replaced. apt-btrfs-parent development

Looking at noatime on etc/fstab rather than the date in the dir
name seems flawed. Changed. Will work on better snapshot management
instead.

etc/apt-btrfs-parent should be a symlink to the previous snapshot.
This will allow rolling back a few snapshots and starting a new
"branch" and keep track of everything. create_root_snapshot is
done, except for tests. set_default to be done next.

AptHistoryLog needs a consolidate method to resume all install/
upgrade/remove/purge info.

Roadmap in TODO
A few fixes and small advances
create_snapshot done, set_default in progress

create_snapshot and its tests work as desired.
set_default needs to snapshot rather than copy, and then must set
the parent link.
parent link set correctly in set_default

delete_snapshot should correct parent link chain
Lots of refactoring

Two utility functions moved into Fstab class.
supported function moved to module root.
functions renamed to better match the names of the commands they
excecute.
AptBtrfsSnapshot.__init__() now mounts the root volume or uses the
test directory indicated by the optional kwarg test_mp.
AptBtrfsSnapshot.__del__() created to umount the root volume on
exit.

Parent link management complete and tested.
rollback function complete and tested.
AptHistory sorting done, consolidation started

Should list packages manually installed using dpkg too. Wondering
how.
dpkg_history is functional. Tests are rather vague though.

Should test individual functions in dpkg_history. Globally it works
and the counts in the test files have been meticulously verified.

Next step: add in information on auto-installed packages.
dpkg_history complete and fully tested. apt-btrfs in flux

Command line needs work.
status command added.

Gives date of parent snapshot and lists of package changes.
DpkgHistory.__add__() done and small bugfixes.

Adding two DpkgHistory instances combines their operation lists
relying on their chronological relationship to choose what to say
for each package. e.g. x installed and then upgraded -> just say
installed and put latest version number.

Assumes there is no overlap between the two. Normally there won't
be.
Small clean-ups
Changes saving on snapshot creation. Done and tested.