Refactored RVar/RDom to avoid redundant data, added support for up to 8 dimensional RDoms.
Reverted un-used changes.
More reverts.
Fixed indent mistake.
Removed unnecessary support for undef ReductionVariables in build_domain.
undef<int> -> Expr()
Merge pull request #461 from halide/rdom-refactor

Rdom refactor