NASM parser: change from Bison parser to hand-written recursive descent

NASM parser: change from Bison parser to hand-written recursive descent
parser with one token of lookahead.  This allows for better error handling
and proper handling of things like "xxxx"/5.  There may be a minor speedup
but it's probably a wash.

Still TODO:
 - Unify the expression parser with the NASM preproc one.
 - Change the GAS parser to recursive descent.

Only had to change one test result; this is due to re-ordering of symrec
creation versus symrec use in data expressions such as x db y.  With the
Bison parser, the symrec use (y) would come first, now the symrec creation
(x) comes first.

svn path=/trunk/yasm/; revision=1716