lavf: Replace the ASF demuxer

The old one is the result of the reverse engineering and guesswork.
The new one has been written following the now-available specification.

This work is part of Outreach Program for Women Summer 2014 activities
for the Libav project.

The fate references had to be changed because the old demuxer truncates
the last frame in some cases, the new one handles it properly.
The seek-test reference is changed because seeking works differently
in the new demuxer. When seeking, the packet is not read from the stream
directly, but it is rather constructed by the demuxer. That is why
position is -1 now in the reference.

Signed-off-by: Anton Khirnov <anton@khirnov.net>

tests/ref/fate/wmv8-drm-nodec

@@ -146,7 +146,6 @@
 0,       6666,       6666,       41,     1349, 0x02adaaf3
 0,       6708,       6708,       41,     1464, 0x20d7cfd2
 0,       6750,       6750,       41,     1377, 0x78e0b1f4
-0,       6791,       6791,       41,      289, 0x1f2e9246
 1,       6878,       6878,        0,     1088, 0x678f20fd
 1,       7161,       7161,        0,     1088, 0x718afa20
 1,       7444,       7444,        0,     1088, 0x758f0939