Avoid too-large shift on 64-bit machines

Shifting a 64-bit value by 64 is undefined, and also causes a GCC
warning.
Be consistent about integer sizes in error message
Re-enable some declarations in abc/kit.h

These avoid implicit declaration problems in code that calls the
functions. Add a note about Kit_SopFactor, whose definition we seem
to be lacking.
Remove obsolete ToSAT cast

Now that we have a proper base class, no cast is needed.
Caught by GCC's -Wstrict-aliasing, though I don't think it could
have ever been a runtime problem.
NULL-initialize conditionally-set pointers

In case there are logic errors, we'll get a clean null dereference
instead of a uninitialized read, and the runtime cost should be
too small to measure.
Also quiets GCC's -Wuninitialized.