Fix for containers with 'const' values

Fix omission of 'const' specifier when generating binding code for
containers whose value type is 'const', which would lead to binding code
that does not compile due to 'const' mismatch. Includes test case.

Change-Id: Iff99a16ee071bb255f78e86e2456e5206cc00cfb
Reviewed-by: John Cummings <jcummings2@users.sf.net>