Consider possible reordering of cursor colors

Was broken on Windows with pdcurses by adding support of Xterm 256
colors.
Fix `:highlight <anything>`

It was treated like `:highlight clear` and vice versa.
Fix comments on overwrite arg in io/iop.h
Work around rename() on Windows

It doesn't overwrite files there.
Fix iop_ln() overwriting on Windows
Implement file copy progress on Windows
Do not run symbolic links tests on Windows

Because creating symbolic links on Windows requires administrator
rights.
Merge branch 'win-ui-and-io-fixes'

Fix:
 * `:highlight <anything>`
 * colors when pdcurses is in use
 * file copying progress on Windows
 * i/o tests on Windows