indeo3: use unaligned reads on reference blocks.

They are not guaranteed to be aligned.
Fixes Bug 503.

CC:libav-stable@libav.org
avconv: remove -deinterlace

It is incompatible with refcounted frames and since it's been deprecated
for a long time now, fixing it is not worth the effort.
configure: make avconv select (a)trim filters

They are now used for -ss/-t
configure: add dependencies to lavfi .pc file

The scale filter depends on sws, resample on lavr, and movie on lavf and
lavc.

Fixes Bug 502.
FATE: use a less ambiguous end time for filter-trim-time test

0.1 seconds at 25 fps is exactly 2.5 frames, which may be rounded either
to 2 or 3 on different platforms.