Serial & TTYStream Buffering Improvements

[Conrad T. Pino]

Hi David,

The Serial & TTYStream classes as written won't operate
very well except in canonical line mode.  My project is
interactive and/or packet oriented since I'm doing real
time data acquisition.

The problems I see in TTYStream are:

1. Method "underflow" doesn't support the unbuffered case.

2. Method "overflow" doesn't support buffer drain without
generating spurious output i.e. a zero byte.

3. Output buffer size synchronized to input buffer size
is problematic for my application.

4. Method "getBufferSize" as implemented not useful for
external buffer allocation in all cases.

5. Methods "flushInput" & "flushOutput" not virtual so
data held by "streambuf" is not flushed properly.

6. Method "isPending" while virtual and overridden didn't
consider data held by "streambuf".

I'm committing a patch that works in interactive mode as
a work in progress.  I'll test packet mode next.  I'll
test line input mode but not extensively.

Please review the patch which follows in a separate message
if serial ports are part of your work.  The above issue list
might not be complete when compared to submitted patch.

Best regards,

Conrad Pino