Two problems with compiling mb on Unix.

1. Makefile contains several lines with a question mark
next to the equal signs. For example, on line 4

ARCHITECTURE ?= unix

By doing a search and replace to change '?=' to '='
this problem was fixed.

2. Running 'make' generated an error saying that
there was an unexpected end of line on line 28

   USEREADLINE = yes

Running 'gmake' instead of 'make' seems to fix this
problem.