Correcting a source file name in the docs just now reminded me that
I've seen a lot of outdated source file names elsewhere in the code,
due to all the reorganisation since we moved to cmake. Here's a giant
pass of trying to make them all accurate again.
sshblowf.h (as was) is 100% internal to that directory. And mpint_i.h
and ecc.h are specialist enough that it's reasonable to ask clients
outside the crypto directory to include them with a subdirectory path,
to hint that it's an unusual thing to be doing.
