Optimise selection.order.

A small optimisation: only call insertBefore() if node.nextSibling isn't
already what we want, so that document nodes that are already in the
correct order can be skipped.
Add test for range clamping.
Fix NaN in clamped log scale inversion.
Fix a bug with entering tick transition.

The tick sizes need to be set, else they grow from zero.
Add d3.behavior.mouse: supports both SVG and HTML.
Rename d3.svg.touches to d3.behavior.touches.
Fix references to d3.behavior.{mouse, touches}.
Fix more references to d3.behavior.{mouse, touches}.
Simplification to spline example.
Merge pull request #441 from jasondavies/spline

Simplification to spline example.
Merge branch 'order' of https://github.com/jasondavies/d3 into release
Fix a bug in circle-packing layout.

There's an edge condition which is not discussed in the original algorithm
("Visualization of Large Hierarchical Data by Circle Packing", Wang et. al):
what happens if the first intersecting circle C_j is equidistant from C_m and
C_n? In other words, it is both after C_n on the front-chain, and before C_m.
The correct answer is that you should splice the smaller of the two circles. If
C_m is smaller than C_n, then splice from C_j to C_n and set C_m to C_j;
otherwise, splice from C_m to C_j, and set C_n to C_j.
Merge branch 'release'
Merge branch 'master' of github.com:mbostock/d3
Fix polylinear descending domains or ranges.

Fixes #446.
allow to specify custom tick positions

Custom positions for ticks can be specified like
ticks([1, 20, 33, 56])
which will give ticks in those positions.
test for tick positions given as list
make check whether array of tick positions is given more restrictive (mbostock)
fix order of checks...
separate variable and accessor method for ticks (mbostock)