event' from master"

Since there is no repeatable test case, and this is obviously wrong, this is
the most conservative change that might possibly work.  

The syscall  read()  wasn't checked for a negative return value for an
interrupted read.  The kernel  sys_read()  returns -EINTR, and the "library" 
layer maps that to return value of -1 and sets  errno  to EINTR.  It's 
impossible (on Linux) for  read()  to set errno EINTR without the return 
value being -1 .

So, if we're checking for EINTR behavior, we should not require that the
return value be zero.


mysys/my_read.c:
  The read() syscall should check for negative one, since that (usually) signals
  errors (like being interrupted) and zero (usually) signals end-of-file .