canonic(): don't use abspath() for filenames looking like <...>; this
fixes the problem reported in SF bug #477023 (Jonathan Mark): "pdb:
unexpected path confuses Emacs".
diff --git a/Lib/bdb.py b/Lib/bdb.py
index 7326a72..29cba80 100644
--- a/Lib/bdb.py
+++ b/Lib/bdb.py
@@ -23,6 +23,8 @@
         self.fncache = {}
 
     def canonic(self, filename):
+        if filename == "<" + filename[1:-1] + ">":
+            return filename
         canonic = self.fncache.get(filename)
         if not canonic:
             canonic = os.path.abspath(filename)