mw.loader.store: do one eval per batch, rather than one per module

Concatenating module implementations and calling $.globalEval on the result is
reproducibly faster for me than calling $.globalEval for each module.

Change-Id: I70e5bcedb43cd1331720a8e5e6c52cfeabb41ab7
Merge "mw.loader.store: do one eval per batch, rather than one per module"