ctf_add_type(): when looking up an integer or floating point type in the
list of pending dynamic type definitions, a match on the type name is not
sufficient - we need to compare the type encodings as well. For example,
bitfields have their own distinct type definitions which share the name of
the underlying integer type, and these types aren't generally
interchangeable.

This bug was causing the following libdtrace error when attempting to trace
the th_flags member of a struct tcphdr:

cg: bad field: off 104 type <32877> bits 539620016

Reported by: rwatson
MFC after: 3 weeks