Warn if flag is in progress

[pannous]

(probably too many) users run into errors like
#31
nodejs/node#2760
etc

Please output warnings when encountering those flags!

node --harmony_modules

import { square, diag } from 'lib';
...
SyntaxError: Unexpected token import

[Knighton910]

Hey at @pannous, did you have any luck with this so far? If not let me know & we will tackle it together 🎱

[evanlucas]

As a general statement, most of the harmony flags should be considered as "in progress". Unless they are enabled by default. A good way to see if something has been shipped would be to run node --v8-options | grep -A1 harmony. If the default shows true, then it should work properly.

[Knighton910]

@pannous did you need anymore help going forward with this?

[subfuzion]

@pannous, in reference to the bug you mentioned, you could run this command node --v8-options | grep "in progress" to see that "harmony modules" is still in progress.

Please be aware that in progress features are incomplete and possibly broken features of V8, so use them at your own risk. By definition, you should only consider the features that are enabled by default (don't require a runtime flag) to be stable features.

Hope this helps clarify things.