Removed the unnecessary premultiplied alpha in CPTGradient. Fixed issue 465.
Removed the unnecessary premultiplied alpha in CPTGradient. Fixed issue 465.

eoinnorris/core-plot,sureshdustrise/core-plot,sureshdustrise/core-plot,divyavamsee/core-plot,LiDechao/core-plot,tectronics/core-plot,zenXian/core-plot,tectronics/core-plot,kamalvenkat/core-plot,divyavamsee/core-plot,tectronics/core-plot,LiDechao/core-plot,eoinnorris/core-plot,sureshdustrise/core-plot,kamalvenkat/core-plot,eoinnorris/core-plot,tectronics/core-plot,LiDechao/core-plot,kamalvenkat/core-plot,eoinnorris/core-plot,zenXian/core-plot,sureshdustrise/core-plot,divyavamsee/core-plot,LiDechao/core-plot,kamalvenkat/core-plot,zenXian/core-plot,zenXian/core-plot,divyavamsee/core-plot