Optimize BaseEventLoop._run_once()
Optimize BaseEventLoop._run_once()

Logger.log() is "slow", logger.isEnabledFor() is faster and the logger is
disabled in most cases. A microbenchmark executing 100,000 dummy tasks is 22%
faster with this change.

See the CPython issue: http://bugs.python.org/issue20275

manipopopo/asyncio,gsb-eng/asyncio,jashandeep-sohi/asyncio,haypo/trollius,gvanrossum/asyncio,gsb-eng/asyncio,ajdavis/asyncio,1st1/asyncio,manipopopo/asyncio,jashandeep-sohi/asyncio,fallen/asyncio,vxgmichel/asyncio,Martiusweb/asyncio,haypo/trollius,1st1/asyncio,vxgmichel/asyncio,Martiusweb/asyncio,manipopopo/asyncio,vxgmichel/asyncio,ajdavis/asyncio,gvanrossum/asyncio,1st1/asyncio,gvanrossum/asyncio,Martiusweb/asyncio,ajdavis/asyncio,jashandeep-sohi/asyncio,fallen/asyncio,haypo/trollius,fallen/asyncio,gsb-eng/asyncio