Patch submission for model strnlen

Hi David,
I have submitted the kf_strnlen patch on the gcc patches mailing list.
Following your suggestion, on the higher verbosity command  make check-gcc
RUNTESTFLAGS="analyzer.exp=strnlen-1.c -v -v", i even identified some new
possible bug flows in my previous patch, which i have fixed in the current
version.
Earlier my bifurcation logic was inside if(lhs_type) which possibly hided
the constraints for non lhs_type calls, so i provided lhs_type for binop
operations block, and made the code flow run through the constraints in
both bifurcation logical paths.

Also, added impl_call_pre to check if a string is checked for
null-teminator before bifurcation.

Looking for your guidance for the provided strnlen patch.

Your sincerely,
Saish Kamabli