Create new files as sparse on NT systems. (2nd try)

[Vaclav Haisman]

> This is consistent with the way the rest of cygwin works, however.  The
> same argument could be applied to testing for ntsec.  If this was an issue
> then we should be changing the fs information to reflect reparse points.
>
> cgf

I am not sure what is the conclusion here. Should I make it check for
FILE_SUPPORTS_SPARSE_FILES even though it can be inaccurate?

Vaclav Haisman