[lmi] wx pre-3.3.0 warning

[Greg Chicares]

Running the automated GUI test with wx pre-3.3.0, I observe:

create_open_database: started
Element wxStaticText@00000000025b85d0 ("X axis", HWND=00000000000a03d6) of 
wxStaticBoxSizer s
hould be created as child of its wxStaticBox and not of 
wxPanel@00000000025b2180 ("panel", HW
ND=00000000000a0440).
Element wxStaticText@000000000259fca0 ("X axis", HWND=00000000000a0476) of 
wxStaticBoxSizer s
hould be created as child of its wxStaticBox and not of 
wxPanel@0000000000cc8f00 ("panel", HW
ND=000000000008009e).
time=569ms (for create_open_database)
create_open_database: ok

and something similar for the 'create_open_strata' test.
Both tests succeed, and the controls seem to work just
fine in my limited manual testing.

As far as I can guess, this pertains to MultiDimGrid::Create():

    // setting self as a wxPanel
    wxPanel::Create(parent, id, pos, size);
    ...
    wxStaticBoxSizer* const sizer =
        new(wx) wxStaticBoxSizer(wxHORIZONTAL, this, "Axis");

where no explicit wxStaticBox is created at all. I'm
disinclined to touch that code. I suspect that the
imperfection now diagnosed has always existed, but
simply wasn't diagnosed in the past, yet AFAICT it
seems benign.