Fix major bug related to multiple handling. Unfortunately this slows down

Fix major bug related to multiple handling.  Unfortunately this slows down
bytecode multiple output significantly, but this way handles generating
relocations correctly (otherwise extern foo; times 5 dd foo doesn't work!).

* bytecode.h (yasm_bc_tobytes): Remove multiple output parameter.
(yasm_bc_get_multiple): New.
* bytecode.c (yasm_bc_tobytes): Update to iterate through multiple here.
(yasm_bc_get_multiple): New.
* xdf-objfmt.c, elf-objfmt.c, bin-objfmt.c, coff-objfmt.c: Don't iterate
through multiple here.
* nasm-listfmt.c: Use yasm_bc_get_multiple() to get multiple instead of
yasm_bc_tobytes().

* bytecode.pxi: Update.

* tests/win32-relocovfl.asm: Tests both this and [1534] but generates too
huge of a file (3MB) to be put into the automated tests.

svn path=/trunk/yasm/; revision=1536