Added a new Rappture.result() function to the Python library.
This makes it easy to finalize results. See examples/graph
for example use.
Added examples/graph to illustrate a simple tool with a string
and two numbers for input.
Fixed the XY graph to show crosshairs and pop-up info when
you mouse over particular points.
Fixed Rappture::exec so that it doesn't add stray newlines when
a program has lots (more than 8k) of output.
Fixed the analyzer to recognize the <tool><analyzer> tag.
When set to "last", this automatically clears the last result.
Handy for programs like SPICE, where you don't compare much,
but keep running one new simulation after another.
Fixed <string> entries to enable the Simulate button after
each editing keystroke.
