Prefix tempdir with bootstrap

This is an urelated change from mgedmin's #204 pull request.
Prefixing is good as it might help figuring out what keeps filling up a temp
dir in case there's a problem.

bootstrap/bootstrap.py

@@ -25,7 +25,7 @@ import tempfile
 
 from optparse import OptionParser
 
-tmpeggs = tempfile.mkdtemp()
+tmpeggs = tempfile.mkdtemp(prefix='bootstrap-')
 
 usage = '''\
 [DESIRED PYTHON FOR BUILDOUT] bootstrap.py [options]