This returns a copy of the scale, such that future modifications to the scale's
domain or range (or other attributes) are isolated from the copy. This is useful
for transitions where you may want to make a copy of a scale before it changes,
such that entering elements can be initialized using the previous copy.
Now you can say d3.time.seconds(start, stop, step), which will return every
step'th second after start (inclusive) and before stop (exclusive). In addition,
you can now pass a range method to the time scale's ticks method, which makes it
easier to generate ticks. For example, x.ticks(d3.time.seconds, 15) will return
15-second ticks, rather than using the automatic default.
First, we were using the wrong space-filling format for %d and equivalent.
Second, we weren't parsing numbers with optional leading spaces correctly.
Yay tests!
The renaming of attributes is totally not worth the hassle of maintaining an
externs file (or using the awkward `foo["bar"]` syntax). The file size
reduction from the advanced optimizations was negligible, besides!
Mike Bostock