use thread method if not main thread

fixes pytest-dev#8

Author: xoviat

pytest_timeout.py

@@ -16,7 +16,7 @@
 import traceback
 from collections import namedtuple
 from distutils.version import LooseVersion
-from threading import current_thread
+from threading import current_thread, main_thread
 from _pytest.config import ExitCode
 from _pytest.outcomes import Failed
 
@@ -198,6 +198,10 @@ def timeout_setup(item):
     params = get_params(item)
     if params.timeout is None or params.timeout <= 0:
         return
+
+    if params.method == "signal" and not (current_thread() is main_thread()):
+        params.method = "thread"
+
     if params.method == "signal":
 
         def handler(signum, frame):