[analyzer;alternate edges] remove puny edges on the same line that span less than 3 columns.

These are legitimate control-flow edges, but visually they add
no value.

Implements <rdar://problem/13941325>.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@182502 91177308-0d34-0410-b5e6-96231b3b80d8