Repair fix-format branch relative to master

Fixes a minor merge conflict that might be slowing down #2000. This ended up being caused by a separate one line change by @jasondavies [here](https://github.com/mbostock/d3/commit/519f258f#diff-6634c8489aac5b3c3f09ae6e3a1d6d58L17) to src/locale/number-format.js as part of commit 519f258f.

This commit merges master into fix-format and repairs that merge-conflict. Confirmed that tests are passing including new tests in test/format/format-test.js I'm not sure what the etiquette is here, so I've taken the more conservative approach of creating this pull request against the pending fix-format branch, assuming jason could merge this into that branch and then #2000 will be ready to go again.