[lmi] Accessing html help while an XRC dialog is active

[Greg Chicares]

Right now, when an XRC dialog is active, only contextual help is
available, but it would be very handy to provide a way to access
html help as well. The main "Contents" page would be enough: it's
not important to open html help to any particular page.

Motivating reason: some text controls accept sequences such as
  10000 3; 0
which represents a vector {10000, 10000, 10000, 0, ... 0} of a
length that's appropriate given the input starting age. These
sequences follow a grammar that many end users don't memorize, so
they'd want to be able to look up the applicable help page while
the dialog is active. It's not important to show that particular
page--they may want to see other pages as well.

I can imagine two methods for accessing html help in this case:

(1) F1 would be ideal IMO. Shift-F1 is already the standard (at
least on msw) keyboard shortcut for contextual help (same as the
[?] box provides), so we don't need F1 to be a synonym. It looks
like the ms spreadsheet behaves this way: F1 != Shift-F1, and F1
has the same effect whether or not a dialog is active.

(2) If (1) isn't possible, then we've got a "Help" pushbutton on
each XRC dialog already, and it's mapped to wxID_HELP, but still
it does nothing. How can it be made to display html help?

If (1) is feasible, then we should ignore (2) and remove the
"Help" pushbuttons from XRC dialogs.