malloc.c: add init function __malloc_init2 with fewer parameters

This simpler interface saves bytes in the initialization code.

Part of fix for issue #2.

Signed-off-by: Ulrich Hecht <ulrich.hecht@gmail.com>
huc: save bytes in ovlentry, load_cd_ovl

To make overlay entry and CD error handler fit in the space before the
boot code even with data and heap initialization.

Part of fix for issue #2.

Signed-off-by: Ulrich Hecht <ulrich.hecht@gmail.com>
huc: startup.asm: pad initialization code to avoid irq handler shift

The overlay entry code does not re-initialize the interrupt handlers,
making it necessary to have them all in one place and thus to pad the
code if there is no data or heap initialization.

Final part of fix for issue #2.

Signed-off-by: Ulrich Hecht <ulrich.hecht@gmail.com>
isolink: Makefile: add dependency on overlay.h

Signed-off-by: Ulrich Hecht <ulrich.hecht@gmail.com>
test: added non-automated overlay test

Test suite emulator TGEmu does not support CDs...

Signed-off-by: Ulrich Hecht <ulrich.hecht@gmail.com>