function makeRequire(mod, enableBuildCallback, altRequire) {
            var relMap = mod && mod.map,
                modRequire = makeContextModuleFunc(altRequire || context.require,
                                                   relMap,
                                                   enableBuildCallback);

            addRequireMethods(modRequire, context, relMap);
            modRequire.isBrowser = isBrowser;

            return modRequire;
        }
Helper function that creates a require function object to give to
modules that ask for it as a dependency. It needs to be specific
per module because of the implication of path mappings that may
need to be relative to the module name.