Reintroduce hasplugin to PytestPluginManager

Fix #932

_pytest/config.py

@@ -211,6 +211,10 @@ class PytestPluginManager(PluginManager):
         # support deprecated naming because plugins (xdist e.g.) use it
         return self.get_plugin(name)
 
+    def hasplugin(self, name):
+        """Return True if the plugin with the given name is registered."""
+        return bool(self.get_plugin(name))
+
     def pytest_configure(self, config):
         # XXX now that the pluginmanager exposes hookimpl(tryfirst...)
         # we should remove tryfirst/trylast as markers

testing/acceptance_test.py

@@ -586,6 +586,11 @@ class TestInvocationVariants:
         assert type(_pytest.config.get_plugin_manager()) is _pytest.config.PytestPluginManager
 
 
+    def test_has_plugin(self, request):
+        """Test hasplugin function of the plugin manager (#932)."""
+        assert request.config.pluginmanager.hasplugin('python')
+
+
 class TestDurations:
     source = """
         import time