remove a too-tight checking of bit rate
Merge pull request #1573 from sijchen/after_review1

[Encoder] remove a too-tight checking of bit rate
add SetOption(ENCODER_OPTION_SVC_ENCODE_PARAM_BASE,&base) for encoder
Merge pull request #1575 from ruil2/set_param

add SetOption(ENCODER_OPTION_SVC_ENCODE_PARAM_BASE,&base) for encoder
Merge remote-tracking branch 'upstream/master' into travis.osx