- Fix much brokenness in absolute value handling, particularly in regards to

- Fix much brokenness in absolute value handling, particularly in regards to
  PC-relative relocations (jumps and calls).
- Allow SEG:OFF to be used as just an offset portion (like NASM does).
- Labels in absolute sections that are declared global are given the correct
  absolute value in the symbol table.

One difference from NASM:
  label equ 0040h:001eh
  jmp label
in NASM means the same as:
  jmp 001eh  (a near jump)
but yasm will treat this the same as:
  jmp 0040h:001eh  (a far jump)

I'm still not completely happy with this implementation, but it's workable
and fixes all the bugs I've found so far in absolute handling.

svn path=/trunk/yasm/; revision=1634