tag: remove docstring about unexistant feature

This was the intention for first creating the subcommand but since we
still don't have a means of removing old data, this docstring is talking
about a ghost.

I'll remember to push for that use case when we implement data removal.

Signed-off-by: Gabriel Filion <gabster@lelutin.ca>
Reviewed-by: Rob Browning <rlb@defaultvalue.org>
Correct claim about number of packs per backup

The current sentence implies that there is only one pack file per backup
run, which is not necessarily correct.

Because of the "constants" max_pack_size and max_pack_objects that are
used as limits to pack sizes, we may end up with more than one pack per
backup if there is a lot of data that needs to be stored.

Signed-off-by: Gabriel Filion <gabster@lelutin.ca>
[rlb@defaultvalue.org: adjust commit summary]
Reviewed-by: Rob Browning <rlb@defaultvalue.org>
index: Correct inconsitency in documentation of modes

In the optspec, --clear and --check are documented as being modes, but
in the man page they are simple options.

Also, even though --clear and --check are listed as modes in the
optspec, they don't appear in the synopsis line.

According to the code, --clear and --check do behave as modes so we
should be consistent in how we document them.

Signed-off-by: Gabriel Filion <gabster@lelutin.ca>
Reviewed-by: Rob Browning <rlb@defaultvalue.org>
Tested-by: Rob Browning <rlb@defaultvalue.org>
Call add_error() with one arg on readlink failure

...instead of two.

This bug and its solution was found by Ben Kelly.

Signed-off-by: Gabriel Filion <gabster@lelutin.ca>
[rlb@defaultvalue.org: adjust commit message]
Reviewed-by: Rob Browning <rlb@defaultvalue.org>
Makefile: Rewrote so that 'make bup' can be up-to-date
bup cat-file: Added --ref option to specify branch or commit hash.

This option uses git's "git rev-parse" functionality, which resolves
ref's such as branches, tags, or commit hashes. If mybranch is the
name of a branch, "bup cat-file --ref=mybranch path/to/myfile" uses
rev-parse to resolve the commit hash of the commit mybranch points to.
This also enables us to use notation like mybranch^ which refers to
the commit preceding the commit pointed to by mybranch (if mybranch
has exactly one parent). Furthermore, if the commit hash is known, it
can be given directly as --ref=myhash.
Added command "bup log"

"bup log" can be used to inspect the backup history.
It is a wrapper for "git log" and "git diff-tree" and uses them in a
way that is convenient for the bup use case. Furthermore, "bup log"
knows about name mangling and will hide the name mangling from the
user, a feature that "git log" cannot provide directly.
The man-page contains detailed information and examples.
Added command "bup pick-saves"

This low-level command generates a new branch.