Partial MDI rewrite

[Dmitry Timoshkov]

Hello all,

here is a result of my work aimed to merge MDI child creation
with common window creation code. The rewrite allows MDI children
to have WS_EX_MDICHILD style set on WM_CREATE and therefore properly
get lParam from MDICREATESTRUCT. MDICREATESTRUCT is now gets A<->W
translated (translation 16-bit windows is still missing).

Please give it a try with your favorite MDI application and report
the results you get.

The patch includes a simple test case, which passes on win9x and
win2000 SP4.

Thanks.