drivers/serial/serial.c open, read, write, and poll methods will not return a...

drivers/serial/serial.c open, read, write, and poll methods will not return a short transfer or an EINTR error if a signal is received while waiting (only)

git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@5022 42af7a65-404d-4744-a932-0658087f49c3