Fix build with MinGW on Windows
Review Request #127266 - Created March 3, 2016 and submitted
Fix building with MinGW on Windows, by removing conflicting FOCUS_EVENT (also "OPTIONAL" and "CreateEvent") defines. Note that there already is a similar #undef in dom2_eventsimpl.h, but this is ineffective, if the Windows defines are added after dom2_eventsimpl.h was (first) included.
First, I tried solving this by shuffling around includes, but gave up on this path after quite some trial and error. (Main route of inclusion for windows.h seems to be khtml_part.h -> parts/browserextension.h -> Platform includes.)
Now builds with MinGW.