Deleting a branch from a repository

[Olin Shivers]

It appears that it is impossible to delete a branch from a repository.
I.e., there's no way to gc a repository and have all unreferenced
storage reclaimed. Is this correct? If so, this seems to be a serious
flaw.

I've poked around on the net and found no answers. The following little
annotated experiment shows my difficulties.
    -Olin

Make a fresh repo:

    % mkdir /var/tmp/sandbox
    % cd /var/tmp/sandbox
    % bzr init-repo .
    Shared repository with trees (format: pack-0.92)
    Location:
      shared repository: .

Create a new branch inside it, a-perm, containing one small file & commit:

    % bzr init a-perm
    Created a repository tree (format: pack-0.92)
    Using shared repository: /var/tmp/sandbox/
    % cd a-perm/
    /var/tmp/sandbox/a-perm
    % echo Hello, world. > foo
    % bzr add foo; bzr commit -m "Created foo"
    adding foo
    Committing to: /var/tmp/sandbox/a-perm/
    added foo
    Committed revision 1.
    % cd ..

Create a second branch, b-tmp, and put a large (64M), incompressible
file in it. Commit.

    % bzr init b-tmp
    Created a repository tree (format: pack-0.92)
    Using shared repository: /var/tmp/sandbox/
    % cd b-tmp
    /var/tmp/sandbox/b-tmp
    % dd if=/dev/urandom of=bar bs=1k count=64k
    65536+0 records in
    65536+0 records out
    67108864 bytes (67 MB) copied, 15.789 s, 4.3 MB/s
    % du -sk .
    65660	.
    % du -sk ../.bzr
    68	../.bzr
    % bzr add bar; bzr commit -m "created bar"
    adding bar
    Committing to: /var/tmp/sandbox/b-tmp/
    added bar
    Committed revision 1.
    % cd ..

Note that the repo is now about 64MB (and so is b-tmp):

    % du -sk .bzr
    65712	.bzr
    % du -sk b-tmp/
    65660	b-tmp/

Now flush b-tmp. Note that the 64MB file is still occupying space in the
actual .bzr repository:

    % rm -rf b-tmp
    % du -sk .bzr
    65712	.bzr
    % ls
    a-perm

Now... how do I reclaim the storage occupied by the deleted branch in the
repo? Will "pack" do it?

    % bzr pack
    % du -sk .
    131420	.

Nope -- it doubles my storage, actually! Hmm... I don't think "pack" means what
the bzr implementors think it means. 

How about "check"?

    % bzr check --repo
    Checking repository at 'file:///var/tmp/sandbox/'.
    checked repository <bzrlib.transport.local.LocalTransport url=file:///var/tmp/sandbox/> format <RepositoryFormatKnitPack1>
	 2 revisions
	 2 file-ids
	 2 unique file texts
	 0 repeated file texts
	 0 unreferenced text versions
    % du -sk .bzr/
    131356	.bzr/
    % 

Nope.