[Portaudio] adding latency parameter to Pa_OpenStream()

[John Lazzaro]

> To include your idea within the existing API, we could pass these to
> Pa_OpenStream as numBuffers:
>
> #define PA_LATENCY_WHATEVER   (0) /* or _NO_OPINION or? */
> #define PA_LATENCY_LOW       (-1)
> #define PA_LATENCY_HIGH      (-2)

No, I wouldn't suggest doing this, at least not for me -- I have no
use for it, since I would always compute a numBuffers value based on
the latency the user supplies, or defaults. But, if the user wants
to push the latency of the system beyond "recommended", I want for
that attempt (via the -latency command-line option) to have the
intended effect, and so I need:

> Should we have a way, besides environment variables, to force a minimum
> latency when the user knows they have unusual capabilities?

this behavior too. This way, the user-interface is consistent, and I
don't need pages of HTML documentation describing "this is how you set
the environment variable if you use bash, this is how you set the 
environment variable under Windows" etc. 

                                                                --jl