Due to limitations in our plugin architecture, the categories plugin
duplicates code from Flot's core for adding a dummy point to snap the y
axis to zero.  We can get rid of this duplication in 0.9; for now we'll
just update the duplicate to match the change in core that introduced
the new 'zero' option.

This also includes a tweak to zero's default.  Previously zero only
received a value if lines were visible; now it always receives a value,
matching the behavior of other contextual options.

Added a format option 'autoscale' that controls whether the given point
is considered when determining an automatic scale.

The lines & bars 'zero' option controls whether autoscale is set on the
dummy point that is inserted to create the series lower-bound.

Area and bar plots normally use a minimum of zero, since their purpose
is to show size, and using an auto-scaled minimum distorts the plot's
meaning.  But this behavior is undesirable in cases where the plot type
is used in more of a decorative sense.

The zero option provides a way to control this behavior.  It defauls to
true for bars and filled lines.

When the placeholder has (or inherits) the HTML 'dir' attribute or CSS
'direction' we get unexpected results from text metrics, resulting in
visual glitches on the axes.

The suggested solution in #716 was to set ltr on the placeholder, but
this introduces its own problems, since the user probably *does* expect
rtl on items like the legend.  So we'll instead set ltr only on the
canvases.

We should review this behavior at some point; rtl is something we need
to handle, not work around.  It also needs to be kept in mind as we move
canvas-text into a plugin.  But for now this solution at least ensures
consistent behavior.

As pointed out in a comment to #832, initializing maxIndex to zero
results in the creation of a single color even when all indexes are
fixed.

Allow the pie chart to redraw on resize or update.

When a pie's labels don't fit within its container, the pie is redrawn
with a smaller radius until the labels fit, or a fixed number of retry
attempts are exhausted. The redraw flag was not reset on success,
however, which prevented the pie from being redrawn again after a resize
or update.

Previously the container dimensions were checked only once, which
prevented the pie from changing in size as its container was resized.

Eliminate uses of $.browser, since it is no longer present in jQuery 1.9, and some of the cases were no longer necessary anyway.

Document the affected versions of opera, and replace $.browser.opera with a line to detect only affected versions

Remove Internet Explorer specific code, that appears to have no impact on actual rendering see bug #905

This addresses #906, the case where a fixed color index on a series
results in the color generator producing one color less than is actually
needed.

Add nonstandard %q datetime specifier for quarters.

Issue: #890: Fix broken behavior for interacting demo

Removed unnecessary canvas skipPositioning flag.

The primary canvas uses position: absolute while the overlay canvas does
not.  This can cause the two to get out of alignment in rare cases when
floating elements are placed near the plot placeholder.  There doesn't
appear to be any reason why the overlay can't also be
absolutely-positioned, so I've just removed the flag entirely.

Also fixed formatting and removed unused change to tickFormatter args.

Updated license headers for #805.

Added licensing information to each file's headers, along with some
minor cleanup.

Update timezone-js and Olson db; list sources in README.md.