finalize 1.12 version, some more adaptation for pytest versions, streamlining tox.ini

xdist/__init__.py

@@ -1,2 +1,2 @@
 #
-__version__ = '1.11'
+__version__ = '1.12'

xdist/plugin.py

@@ -45,7 +45,11 @@ def pytest_addoption(parser):
 # -------------------------------------------------------------------------
 def pytest_addhooks(pluginmanager):
     from xdist import newhooks
-    pluginmanager.addhooks(newhooks)
+    # avoid warnings with pytest-2.8
+    method = getattr(pluginmanager, "add_hookspecs", None)
+    if method is None:
+        method = pluginmanager.addhooks
+    method(newhooks)
 
 # -------------------------------------------------------------------------
 # distributed testing initialization