Make obsolete source package removal slightly more intelligent

Previously a package which became obsolete during a run would not be
automatically removed until the next run. This was due to the fact that
sources[][BINARIES] is not updated during the run. Instead, we build a
list of source packages which produce at least one binary and then
remove any packages not in that list.

Signed-off-by: Adam D. Barratt <adam@adam-barratt.org.uk>

britney.py

@@ -2418,11 +2418,20 @@ class Britney(object):
         self.auto_hinter()
 
         # obsolete source packages
+        # a package is obsolete if none of the binary packages in testing
+        # are built by it
         self.__log("> Removing obsolete source packages from testing", type="I")
         removals = []
+        # local copies for performance
         sources = self.sources['testing']
-        removals = [ HintItem("-%s/%s" % (source, sources[source][VERSION])) for \
-                     source in sources if len(sources[source][BINARIES]) == 0 ]
+        binaries = self.binaries['testing']
+        used = set(binaries[arch][0][binary][SOURCE]
+                     for arch in binaries
+                     for binary in binaries[arch][0]
+                  )
+        removals = [ HintItem("-%s/%s" % (source, sources[source][VERSION]))
+                     for source in sources if source not in used
+                   ]
         if len(removals) > 0:
             self.output_write("Removing obsolete source packages from testing (%d):\n" % (len(removals)))
             self.do_all(actions=removals)