The xml output is dirty and marked as FIXME

The xml output is dirty and marked as FIXME

The xml output does not use output file as all other outputs, it
has sections here and there while everything is supposed to be in
output.c, and finally the unnecessary field analysis loop made
program about 20% slower when xml was not asked.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>