simplify key setup.
(F): Deleted all but one definitions of the F function/macro.
Added a context argument, and use that to find the subkeys.
(R): Added context argument, and use that to find the subkeys.
(blowfish_set_key): Some simplification.

(encrypt): Deleted code for non-standard number of rounds. Deleted
a bunch of local variables. Using the context pointer for
everything should consume less registers.
(decrypt): Likewise.

Rev: src/nettle/blowfish.c:1.3