Semantics and output of new source-bundle command

Some issues I have with the new bst source-bundle command are as follows:

• I dont like the name argument for the output of bst source-bundle, it could be changed by a simple mangle of the target element, similar to how we compose artifact paths and log file names (e.g. core/totem.bst could become core-totem.tar.gz, no need for an option here)
• Should be able to specify an output directory, defaulting to current working directory
• The resulting tarball contains a tempdir, yuck.

For the last, I ended up creating a test.tar.gz of bst source-bundle --except base.bst core/totem.bst

When I unpacked it, it contained a core-totem-hp1rrdow/ directory... firstly this is ugly, and secondly it means that two runs of bst source-bundle will never produce the same output.