Ability to specify different clock rate when opening sound device in PJSUA-LIB

[nanang]

Attachment 'ticket495.patch':

• added snd_clock_rate to pjsua_media_config
• added command line option --snd-clock-rate
• changed resampler option to follow pjsua quality option

[bennylp]

Committed in r1823, thanks.

[bennylp]

In r1855:

• snd_clock_rate is now initialized to zero in pjsua_media_config_default()
• When trying to open sound device with different clock rate in pjsua_media.c, also try to create resample port and only break successfully from the loop if both sound device and resample port can be created. This is necessary because sometimes resampling is disabled (e.g. in WinCE port).