Patch highWaterMark fix from 0.11.7

Hello @evansolomon, 

Please review the following commits I made in branch 'es-highwatermark'.

91636e5d8d8600713d67d91e2ec01dfb5f2d84cb (2014-03-27 15:55:26 -0400)
Patch highWaterMark fix from 0.11.7
Makes backpressure behave sanely.

R=@evansolomon