Function Builder: dev testing (round 4)

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Function Builder is complete, and is currently being reviewed by the design team (see phetsims/function-builder#86). Once that issue (and any resulting issues) are closed, we can proceed with a (final?) round of dev testing. That will hopefully happen no later than Monday, 7/11/16.

When we're ready to begin, I'll create the dev version, provide instructions, etc.

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There were no significant code changes required for the final change requests (#86). And the previous round of dev testing (#628) found no issues. So we've decided not to do another round of dev testing, and proceed directly to RC testing.

Closing.