add greenlib module for backward compatibility; mark it as deprecated

eventlet/greenlib.py

@@ -0,0 +1,20 @@
+from eventlet.api import Greenlet
+
+class SwitchingToDeadGreenlet(Exception):
+    pass
+
+def switch(other=None, value=None, exc=None):
+    self = Greenlet.getcurrent()
+    if other is None:
+        other = self.parent
+    if other is None:
+        other = self
+    if not (other or hasattr(other, 'run')):
+        raise SwitchingToDeadGreenlet("Switching to dead greenlet %r %r %r" % (other, value, exc))
+    if exc:
+        return other.throw(exc)
+    else:
+        return other.switch(value)        
+
+import warnings
+warnings.warn("greenlib is deprecated; use greenlet methods directly", DeprecationWarning, stacklevel=2)