description:
interactivity issue for radar chart.

build number:
2.6.0.v20100330-0630

steps to reproduce:
1. new a chart, select type as radar, go to "format chart" tab.
2. go to "series->value series".
3. go to "chart area", tick "enable chart interactivity", go to "series->value series" and go back to "chart area".

expected result:
1. if the interactivity can not be used, the "interactivity" button should be invisible.
2. the status of "enable chart interactivity" can be remembered.

actual result:
1. in step 2, "interactivity" button is disabled.
2. in step 3, "enable chart interactivity" is untick.

error log:
n/a
added interactivity support in radar example chart
also fixed some ui bugs.
verified in build (2.6.0.v20100406-0630), closed.