[CFT] Windows native file/folder picker (fop/fps)

[Michael Stahl]

hi all,

some weeks ago on master (5142e628b563a9876e8884c5dd4914eff4a2f307) i've
merged 2 Windows-only DLLs, namely the contents of the "fop" library
into "fps":  "fop" implements a native Windows folder picker, while
"fps" implements a native Windows file picker; now both file and folder
picker are implemented by "fps" library.

it would be great if somebody could test if both native folder and file
picker still work as they did before (e.g. compare with 3.5 branch) on
the various supported Windows releases.