newt - Prevent hang on simultaneous compile error.
newt - Prevent hang on simultaneous compile error.

The stop channel only had capacity for one entry.  If two go routines
fail at the same time, they both try to enqueue to the stop channel,
causing the second thread to block.

The fix is to give the stop channel more capacity.  Change it from 1 to
num-threads.

apache/incubator-mynewt-newt,apache/incubator-mynewt-newt