Fix a regression when no options are provided.
Added a width parameter to control text wrapping.

The optional width parameter establishes a maximum width for the text's
bounding box, forcing it to wrap when it reaches that size.
Restore 0.7's maximum width for x-axis labels.

Flot 0.7 calculated x-axis label dimensions by assigning each label a
fixed width, then measuring the height as determined by the browser.  A
side-effect of this technique is that x-axis label divs received a fixed
width.  The rewrite of the text system in 0.8 accidentally removed this
feature; this patch restores it.