fix handling of corrupt collections on windows

- advise user to create new profile, which prevents restores from
  backup overwriting old backups
- don't rename the collection file, as it's no longer necessary,
  and it fixes a windows bug where the main window would be left
  open due to a failure to rename the locked collection file

aqt/main.py

@@ -271,14 +271,13 @@ To import into a password protected profile, please open the profile before atte
             self.col = Collection(cpath, log=True)
         except anki.db.Error:
             # warn user
-            showWarning("""\
-Your collection is corrupt. Please see the manual for \
-how to restore from a backup."""+"\n\n"+_("Debug info:")+"\n"+traceback.format_exc())
-            # move it out of the way so the profile can be used again
-            newpath = cpath+str(intTime())
-            os.rename(cpath, newpath)
-            # then close
-            sys.exit(1)
+            showWarning(_("""\
+Your collection is corrupt. Please create a new profile, then \
+see the manual for how to restore from an automatic backup.
+
+Debug info:
+""")+traceback.format_exc())
+            self.unloadProfile()
         except Exception, e:
             # the custom exception handler won't catch this if we immediately
             # unload, so we have to manually handle it