Permit != as a synonym for <>
Stop spurious disassembly with .word '*'

Now that instructions might have their top bit set (type2 instructions), they
can be negative if treated as signed 32-bit integers. This change revealed a
weakness in the heuristic for is_printable(), which this commit mends.
First mostly-unvetted implementation of hw type2

Looks not to be much slower in Spartan6 (because the 5-input XOR is just
one additional layer of LUT6 ?) but functionality has not yet been
tested.
Makefile builds instead of Tcl ones

Various cosmetics changes, rebuilt Xilinx files

EIB included in project, but disabled by default (doesn't compile right now
anyway).

SERIAL no longer explicitly disabled (leave to environment).
Corrections and changes to video display hardware

Make text RAM start at base of video address space:

It's silly to reserve configuration register space at the bottom of the VRAM
address space. Instead, reserve a 4K block and put the registers at the top of
that.

There was apparently an RTL bug meaning the video RAM for the first 16 bytes
(supposed to be reserved for MMRs) was already addressing the text. This mends
that.

Mend garbage being written to display memory:

Since 1ad2eb2 which silenced a warning about bus widths mismatching, garbage
would be written to the display on basically every memory write, because
ramwrap.v was not enabled for only the area of memory devoted to the display :
it simply mapped the bottom 12 bits of the address to itself, and ignored the
bits above it.

bm_mults.texe now shows correct numbers on FPGA hardware, but exposes the fact
that current hardware does not know how to halt. The `illegal` instruction is
treated as a throw to a high (or negative) address, which overflows back to 0
and runs the code again. For now, halts should be replaced with infinite loops
while we consider how to implement software-initiated halt properly.

Mend bug with overlapping MMR and VRAM:

MMR reads were returning zero due to clashing values ; writes worked by
accident.

Now init_display clears the entire display.
Spin when done until we have hardware halt
Simple minutes-seconds clock

The empirically-determined constants imply that the current implementation in
Spartan6 executes about 1070*1780*3=5713800 instructions per second.