Error when using "shape" as a type

Summary: At least one person tried to do this.

Fixes https://github.com/facebook/hhvm/issues/3170

Reviewed By: @int3

Differential Revision: D1674539

Signature: t1:1674539:1415945723:4dc8265faf91bc34b239b78d9b2e8d113611ce84
Conversion for AT composites

Summary: Kinda ugly, but since there aren't too many composites this
will do.

Reviewed By: @ptarjan

Differential Revision: D1673940

Signature: t1:1673940:1415958643:ea838fbb8c51b9645f90d73b2ac356df69449ee4