Make development version format comply with PEP 440.
Make development version format comply with PEP 440.

Formerly we did

    0.1a20150918-32-g829b37a-dirty

Now we do

    0.1a20150918.32+g829b37a-dirty

in order to avoid hyphens before the local version after the `+',
which PEP 440 doesn't like.

probcomp/bdbcontrib,probcomp/bdbcontrib