Extend the input types for CBB_add_*() to help catch bugs.

Extend the input types for CBB_add_*() to help catch bugs.

While the previous types were correct, they can silently accept bad data
via truncation or signed conversion.  We now take size_t as input for
CBB_add_u*() and do a range check.

discussed with deraadt@
input + ok jsing@ miod@