Handle classes without save_results

If an analysis class have no save_results function we simply dump a 
pickel file with the name of the class.

cli_main.py

@@ -17,6 +17,7 @@
 import importlib
 import inspect
 import re
+import pickle
 import sys
 import warnings
 from collections import defaultdict
@@ -516,23 +517,19 @@ def main(
     analysis_kwargs.pop("func")
 
     ac = analysis_callable(**analysis_kwargs)
-    results = ac.run(start=startframe,
-                     stop=stopframe,
-                     step=step,
-                     verbose=verbose)
-
-    # prototype lines to test functionality TO REMOVE
-    print(analysis_kwargs)
-    sys.exit("Analysis complete. exiting...")
-    # extract results?
-    # here the same, how are the results collected?
-    # for RMSD we need to access the 'rmsd' attribute after .run() method.
-    # do we need to alter (add) a common interface on all the MDAnalysis
-    # interfaces. This would imply a intervention on the MDA code itself.
-    # we can definitively create a common method on all classes that links
-    # to the classes specific method/attribute where the results are stored.
-
-    save_results_to_some_file(results)
+    ac.run(start=startframe,
+           stop=stopframe,
+           step=step,
+           verbose=verbose)
+
+    try:
+        ac.save_results()
+    except AttributeError:
+        fname = analysis_callable.__name__ + ".pickle"
+        warnings.warn("No specific saving function."
+                      "Pickling results into `{}`.".format(fname))
+        with open(fname, "wb") as f:
+            pickle.dump(ac, f)
 
 
 def maincli(ap):

tests/test_cli_main.py

@@ -9,10 +9,13 @@
 import pytest
 import sys
 
+from MDAnalysis.analysis.rdf import InterRDF
+from MDAnalysis.tests.datafiles import PSF, DCD
+
 # Workaround since we have no real module
 sys.path.append("..")
 
-from cli_main import convert_str_time
+from cli_main import convert_str_time, main
 
 
 @pytest.mark.parametrize('x, frame',
@@ -32,3 +35,24 @@ def test_convert_str_time_dt():
 def test_convert_str_time_raise():
     with pytest.raises(ValueError):
         convert_str_time('0.1', dt=1)
+
+
+class TestMain(object):
+
+    @pytest.fixture()
+    def kwargs(self):
+        kwargs = {}
+        kwargs["begin"] = "0"
+        kwargs["end"] = "1"
+        kwargs["dt"] = "1"
+        kwargs["verbose"] = False
+        kwargs["g1"] = "all"
+        kwargs["g2"] = "all"
+        kwargs["func"] = None
+        return kwargs
+
+    def test_pickling(self, kwargs, tmpdir):
+        with tmpdir.as_cwd():
+            with pytest.warns(UserWarning):
+                main(PSF, DCD, analysis_callable=InterRDF, **kwargs)
+                open("{}.pickle".format(InterRDF.__name__))