Add comments indicating which Windows version returns a given error code.

Moved the file overlapped flag check to default_fd_queue_async.

Before calling the PSN_SETACTIVE in PROPSHEET_SetCurSel set the
active_page to -1. This prevents crashes and corruption of the
property sheet if the application makes any modifications during the
PSN_SETACTIVE.

winedbg: When reloading real PE modules from a minidump, also look in the search path (as we do for ELF modules).

Effectively work out if we are interested in a file before worrying
about prompting for copy or overwrite.