Make log about unavailability of nonblocking sockets log_warn()
Lack of nonblocking sockets can have bad effects when they are needed. Currently fc_nonblock() uses just log_debug() to inform user about this when it happens. Turn that log to log_warn() in S3_1 and master (where warn level exist). S3_0 should probably go to log_normal() (and not all the way to log_error())?
Going to push S3_0 patch to S2_6 too, to help diagnose problems when porting to new platforms.