xulrunner should depend on yasm

[Alexey Fisher]

current xulrunner-2.0 shipped without asm optimisations. You can see it
mostly on video performance. If you play webm  video, it well consume
80% of modern CPU. some debuging with kernel/perf tool show not
optimised vp8 functions.

jast adding yasm to debian/control  and recompile give match better
results.

Here is trace of optimised xulrunner-2.0.

# Overhead      Command                  Shared Object  Symbol
# ........  ...........  .............................  ......
#
    12.53%  firefox-4.0  libxul.so                      [.]
FastConvertYUVToRGB32Row
     8.32%  firefox-4.0  libxul.so                      [.]
vp8_decode_mb_tokens
     7.13%  firefox-4.0  libc-2.12.so                   [.] memcpy
     5.01%  firefox-4.0  [kernel.kallsyms]              [k] clear_page_c
     3.92%  firefox-4.0  libxul.so                      [.]
vp8_mbloop_filter_vertical_edge_mmx
     3.42%  firefox-4.0  [kernel.kallsyms]              [k]
copy_user_generic_string
     3.26%  firefox-4.0  libxul.so                      [.]
vp8_mbloop_filter_vertical_edge_sse2
     2.31%  firefox-4.0  libxul.so                      [.]
vp8_copy_mem8x8_mmx
     2.20%  firefox-4.0  libxul.so                      [.]
vp8_copy_mem16x16_sse2
     1.81%  firefox-4.0  libxul.so                      [.]
vp8_loop_filter_vertical_edge_sse2
     1.65%  firefox-4.0  libxul.so                      [.]
vp8_decode_mb_row
     1.61%  firefox-4.0  [kernel.kallsyms]              [k] page_fault
     1.50%  firefox-4.0  libxul.so                      [.]
vp8dx_decode_bool


Suddenly it is not comparable with mplayer using libvpx0.

Please add yasm to dependencies and ship optimised version.

Thank you for your work.

Regards,
Alexey