Provide raw H.264 output from screenrecord

This adds an experimental (undocumented) "--raw" flag.  If set, we
output an H.264 byte stream rather than a .mp4 file.

If the filename is "-", we send the output to stdout.  If stdout is a
tty, we reconfigure it to avoid CRLF line termination over adb.

Change-Id: I5193f6193c9c1a59f92eefad0ed399f24afbf6de