- make importorskip static at py.test.importorskip because it's

used for conditional plugin loading
- fix case where xfail is defined at module/class level
- fixes and improvements to docs, correct links to plugins
- use new skip facilities here and there

--HG--
branch : trunk

py/__init__.py

@@ -53,6 +53,7 @@ _py.apipkg.initpkg(__name__, dict(
         '_PluginManager'    : '_py.test.pluginmanager:PluginManager',
         'raises'            : '_py.test.outcome:raises',
         'skip'              : '_py.test.outcome:skip',
+        'importorskip'      : '_py.test.outcome:importorskip',
         'fail'              : '_py.test.outcome:fail',
         'exit'              : '_py.test.outcome:exit',
         # configuration/initialization related test api