Add an assert to the compiler for map sizes.
Add an assert to the compiler for map sizes.

We require that they are a power of 2, otherwise we have to fall
back to a slow % operator, instead of &.

baldwinn860/gapid,google/agi,google/gapid,google/gapid,google/gapid,google/agi,pmuetschard/gapid,baldwinn860/gapid,Qining/gapid,google/gapid,baldwinn860/gapid,pmuetschard/gapid,Qining/gapid,pmuetschard/gapid,baldwinn860/gapid,google/gapid,google/agi,google/agi,google/gapid,baldwinn860/gapid,Qining/gapid,google/agi,Qining/gapid,pmuetschard/gapid,pmuetschard/gapid,baldwinn860/gapid,google/agi,baldwinn860/gapid,Qining/gapid,google/agi,baldwinn860/gapid,pmuetschard/gapid,pmuetschard/gapid,google/gapid,Qining/gapid,google/gapid,Qining/gapid,pmuetschard/gapid,google/agi,Qining/gapid