Configuration option to use high quality tone generation

[bennylp]

The tone generator heavily depends on the quality of sine wave generation, and PJMEDIA uses a sine wave emulation which previously thought to give good balance between quality and speed. With this method, speed definitely is much better than using <math.h>, but quality, well turns out not to be perfect.

Norman Franke reported on pjsip list:

Perhaps there should be an option to use a better one, since this one is incompatible with some remote systems. Oddly, it seemed some digits would work, like zero. Nine seemed to be a constant problem, which uses a higher frequency

We should have something like PJMEDIA_USE_HIGH_QUALITY_TONEGEN to activate the tonegen generation using <math.h>, and default should be enabled.

[nanang]

Enable high quality tone generator by default.

[bennylp]

Committed patch as is in r1859, thanks.