Fix #350: Avoid caching ToolTipText failures:

When the internal timeout is hit (when the timeout works) a ToolTipText of '(loading description...)' is shown. Using lazy here means that even when retrying later, this will still be shown.
I made it a function that looks up the result every time. I looked at the corresponding code in FSC, and it will cache the result.
Merge pull request #449 from rojepp/fix_350

Fix #350: Avoid caching ToolTipText failures:
Merge pull request #451 from fsharp/master

merge changes from master