When a location expression requests a register check that we have as
many bytes in the register as requested and if we don't report the
error.
Updates #1416
Change memCache so that the preloaded memory is not read immediately
but only after the actual read to the preloaded range.
This allows us to request caching the entire stack frame every time we
create an eval scope and no unnecessary reads will be made even if the
user is just trying to evaluate a global variable.
