Support require() calls in reduce functions

[tetsuo]

CouchDB does not support require() calls in reduce functions.

We can inline everything into a single bundle for only reduce functions.

[tetsuo]

Something like the following:

if (d === entry.exports.reduce) {
    return (new Promise((packResolve, packReject) => {
        /* TODO: handle errors in here (use pumpify) */
        from.obj(entry.resolvedDeps
            .concat({ ...entry, ...{ source: 'module.exports=' + entry.exports.reduce } } as any))
            .pipe(browserPack({ hasExports: false, raw: true }))
            .pipe(concat(data => {
                let src = data.toString()
                const lines = src.split('\n')
                let last = lines[lines.length - 2]
                last = last.replace(/\;$/, `("${entry.file}")(keys, values, rereduce);`)
                lines.splice(lines.length - 2, 1, last)
                src = 'function (keys, values, rereduce) {' + lines.join('\n') + '}'
                packResolve(src)
            }))
    }))
}

(uses browser-pack)