Do not emit progress if stderr is not a tty

Avoids logging progress data into cron logs, etc.

Suggested-by: Michael Richardson <mcr@sandelman.ottawa.on.ca>
Change-Id: I4eefa2c282f0ca0a95a0185612b52e2146669e4c
Signed-off-by: Shawn O. Pearce <sop@google.com>
1 file changed