format.

Make swscale-test only perform the test from the input to the output
format rather than perform all.

Also implement swscale-test-all.sh, for performing all the tests.

Improve flexibility of the swscale-test tool, this way is simpler to
perform only a subset of tests.

git-svn-id: file:///var/local/repositories/mplayer/trunk/libswscale@30825 b3059339-0415-0410-9bf9-f77b7e298cf2