define was just a local variable. Actually unset the global define when requiring a Node module.
Looks like there was no test for this behavior. I'd add it but not quite sure where to start.
This fixes TypeError: ESP.parse is not a function output in test runs, see this Travis build for an example. In this case Intern uses loader to load a custom reporter, which then requires istanbul/lib/instrumenter. This module requires esprima which erroneously selects the AMD loader.
TypeError: ESP.parse is not a function
fix how global define is unset
`define` was just a local variable. Actually unset the global `define` when
requiring a Node module.