Added support for a new (well, I've run it locally for a year or two)

Added support for a new (well, I've run it locally for a year or two)
interrupt system which is a prerequisite for the Amiga ISA support.
It is described in amiga/amiga/README.ints, and is enabled by adding
an "options IPL_REMAP_1" in the kernel config file.  Along with this
change there is also some generic cleanup, like style polishing,
comment corrections, making sicallbacks operate in FIFO manner and
cleaning up the spl mess in param.h...