Pre-append $B2dir/pythonX(.Y) to sys.path if it exists

This allows britney to load a python2.7 variant of the C module when
run under python2.7.

Note for python3, we add "python3" rather than "python3.Y".  This is
to reflect the include path in the python3 package in the archive.

Signed-off-by: Niels Thykier <niels@thykier.net>

britney.py

@@ -190,12 +190,30 @@ import urllib
 
 import apt_pkg
 
+from functools import reduce
+from operator import attrgetter
+
+if __name__ == '__main__':
+    # Check if there is a python-search dir for this version of
+    # python.  If so, use the britney module for that.
+    import os
+    mdir = os.path.dirname(sys.argv[0])
+    if sys.version_info[0] == 3:
+        python_dir = "python3"
+    else:
+        python_dir = "python2.%d" % (sys.version_info[1])
+    idir = os.path.join(mdir, python_dir)
+    if os.path.isdir(idir):
+        print "N: Loading from %s" % python_dir
+        # Insert in front (else current dir is before it, which makes
+        # it useless).
+        sys.path.insert(0, idir)
+
 from excuse import Excuse
 from migrationitem import MigrationItem, HintItem
 from hints import HintCollection
 from britney import buildSystem
-from functools import reduce
-from operator import attrgetter
+
 
 __author__ = 'Fabio Tranchitella and the Debian Release Team'
 __version__ = '2.0'