[CFLAA] Ignore non-pointers, move Attrs to graph nodes.

This patch makes CFLAA ignore non-pointer values, since we can now
sanely do that with the escaping/unknown attributes. Additionally,
StratifiedAttrs make more sense to sit on nodes than edges (since
they're properties of values, and ultimately end up on the nodes of
StratifiedSets). So, this patch puts said attributes on nodes.

Patch by Jia Chen.

Differential Revision: http://reviews.llvm.org/D21387

llvm-svn: 272833