Make jmp with seg:off equ behave the same as NASM.

Make jmp with seg:off equ behave the same as NASM.
Formerly:
  foo equ 1:2
  jmp foo
would result in a far jump.  Now, an explicit "far" is required:
  jmp far foo
to generate a far jump.

In addition, the direct use of seg:off in immediates and effective
addresses will result in an error; the use of EQU'ed seg:off values
is still legal (and will still result in just the offset).  This
behavior is more sane and also matches NASM behavior.
Thus:
  foo equ 1:2
  mov ax, foo   ; okay, just 2
  mov ax, [foo] ; okay, just 2
  mov ax, 1:2   ; illegal
  mov ax, [1:2] ; illegal

svn path=/trunk/yasm/; revision=2028