fixes #530. I earlier tried this twice (see #530 for history) and then twice rolled it back due to some problems that arose. However, I didn't write down what the problems were in enough detail on the ticket that I can tell today whether those problems are still issues, so here goes the third attempt. (I did write down on the ticket that it would not create site.py or .pth files in the target directory with --multi-version mode, but I didn't explain why *that* was a problem.)
# (See http://tahoe-lafs.org/trac/tahoe-lafs/ticket/142 .)
[aliases]
-build = darcsver --count-all-patches develop --prefix=support make_executable build
+build = darcsver --count-all-patches develop --multi-version --prefix=support make_executable build
test = darcsver --count-all-patches develop --prefix=support make_executable build trial
sdist = darcsver --count-all-patches sdist
install = darcsver --count-all-patches install
keygen_tac = """
# -*- python -*-
+import pkg_resources
+pkg_resources.require('allmydata-tahoe')
+
from allmydata import key_generator
from twisted.application import service