Consolidate almost all lib/crypto/krb headers into a single

Consolidate almost all lib/crypto/krb headers into a single
crypto_int.h.  In that header, define and document responsibilities
for crypto modules, some of which are satisfied through a
module-specific crypto_mod.h.  In the OpenSSL and NSS modules, remove
many of the headers and sources providing functionality which isn't
needed by lib/crypto/krb any more (direct interfaces to MD4, MD5, and
SHA-1 hashing, as well as DES weak key testing).  Change most
Makefile.ins to only include headers from lib/crypto/krb and
lib/crypto/$(CRYPTO_IMPL), instead of from many different directories.

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@24677 dc483132-0cff-0310-8789-dd5450dbe970