fix cubic/line intersection; add skp tests

BUG=skia:2488
TBR=reed

Author: caryclark@google.com

Review URL: https://codereview.chromium.org/252243003

git-svn-id: http://skia.googlecode.com/svn/trunk@14458 2bbb7eff-a529-9590-31e7-b0007b416f81
5 files changed