if hintsdir is defined, read hints from there

This introduces a new variable HINTSDIR, which overrides the location of the
Hints dir (normally it is read from the UNSTABLE dir).

Please note that this is the location of the dir that contains the Hints dir.

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

britney.py

@@ -256,7 +256,10 @@ class Britney(object):
         apt_pkg.init()
         self.sources = {}
         self.binaries = {}
-        self.hints = self.read_hints(self.options.unstable)
+        try:
+            self.hints = self.read_hints(self.options.hintsdir)
+        except AttributeError:
+            self.hints = self.read_hints(self.options.unstable)
 
         if self.options.nuninst_cache:
             self.__log("Not building the list of non-installable packages, as requested", type="I")