python: Remove find_message_by_filename workaround

Now that notmuch_database_find_message_by_filename works on read-only
databases, remove the workaround that disabled it on read-write
databases.

This also adds a regression test for find_message_by_filename.

bindings/python/notmuch/database.py

@@ -526,19 +526,10 @@ class Database(object):
                  retry.
         :raises: :exc:`NotInitializedError` if the database was not
                  intitialized.
-        :raises: :exc:`ReadOnlyDatabaseError` if the database has not been
-                 opened in read-write mode
 
         *Added in notmuch 0.9*"""
         self._assert_db_is_initialized()
 
-        # work around libnotmuch calling exit(3), see
-        # id:20120221002921.8534.57091@thinkbox.jade-hamburg.de
-        # TODO: remove once this issue is resolved
-        if self.mode != Database.MODE.READ_WRITE:
-            raise ReadOnlyDatabaseError('The database has to be opened in '
-                                        'read-write mode for get_directory')
-
         msg_p = NotmuchMessageP()
         status = Database._find_message_by_filename(self._db, _str(filename),
                                                     byref(msg_p))

test/python

@@ -28,4 +28,12 @@ EOF
 notmuch search --sort=oldest-first --output=messages tag:inbox | sed s/^id:// > EXPECTED
 test_expect_equal_file OUTPUT EXPECTED
 
+test_begin_subtest "get non-existent file"
+test_python <<EOF
+import notmuch
+db = notmuch.Database(mode=notmuch.Database.MODE.READ_ONLY)
+print db.find_message_by_filename("i-dont-exist")
+EOF
+test_expect_equal "$(cat OUTPUT)" "None"
+
 test_done