Update systemjs export emit to support new bulk export variation

[mhegazy]

see ModuleLoader/es-module-loader#386 for more details about the fix.

[mhegazy]

@vladima We need to decide if this is a 1.5.2 issue or a 1.6 issue.

[vladima]

Given that current estimate for patch that will include bulk export support in es6 module loader is somewhere after forthcoming release I'd say that having this item fixed in 1.6 should be ok. I've asked @guybedford for more accurate timings, we can always reconsider this decision based on his answer

[mhegazy]

Users will need to update to latest System.js/JSPM

[guybedford]

TypeScript was only supported in SystemJS 0.17, which had the bulk export handling in place, so this shouldn't be breaking for TypeScript users of SystemJS.

[mhegazy]

I believe TypeScript support was added in release v0.17.0, where as the bulk export was added in release v0.17.1. @guybedford would it be safe to assume no one is using 0.17.0?

[guybedford]

Yes there was a ~10 day release window where 0.17.0 was the primary release for TypeScript testing. Because it's a patch upgrade, and the TypeScript support was clearly indicated as a new in-progress feature, I see no issue with including this in TypeScript and allowing the break for that tiny segment, who can simply do a patch update. Strictly it is a breaking change though for this segment, so can certainly be worth documenting according to what fits into your process there.