started implementing bit variants.

not used in the analyzer yet, eventually they should help to improve out bit operation precision.
now computes a single bit variant based on the constant bits
bit variant test also works for 0..1 interval
slightly rewrote bitVariants to allow for recursion
have stub for multi-recursion (returning the single default)
seem to be able to retrieve bit variants
added bitvariant to interval (for later evaluation)
seem to have precise BitVariant computation now
fixed bug in BitVariant computation