Fix bug computing FRAMES in rd_collect_vtm.sh.
Fix bug computing FRAMES in rd_collect_vtm.sh.

Certain Y4M files are detected by grep as binary which prints an error
message and incorrectly sets FRAMES=1. This patch forces binary files
to be interpreted as text by grep to compute correct number of frames.

xiph/daala,ycho/daala,ycho/daala,ycho/daala,xiph/daala,xiph/daala,ycho/daala,xiph/daala,xiph/daala,ycho/daala