Jedi was able to go crazy and loop endlessly in certain if/self assignment combinations.

Here we limit type inferance per tree scope. I'm still not sure this is the way
to go, but it looks okay for now and we can still go anther way in the future.
Tests are there.

Fixes #929.

test/completion/stdlib.py

@@ -236,3 +236,16 @@ import contextlib
 with contextlib.closing('asd') as string:
     #? str()
     string
+
+# -----------------
+# shlex
+# -----------------
+
+# Github issue #929
+import shlex
+qsplit = shlex.split("foo, ferwerwerw werw werw e")
+for part in qsplit:
+    #? str() None
+    part
+    #? str() None
+    part