libctf: hashing

libctf: hashing

libctf maintains two distinct hash ADTs, one (ctf_dynhash) for wrapping
dynamically-generated unknown-sized hashes during CTF file construction,
one (ctf_hash) for wrapping unchanging hashes whose size is known at
creation time for reading CTF files that were previously created.

In the binutils implementation, these are both fairly thin wrappers
around libiberty hashtab.

Unusually, this code is not kept synchronized with libdtrace-ctf,
due to its dependence on libiberty hashtab.

libctf/
	* ctf-hash.c: New file.
	* ctf-impl.h: New declarations.