Win32: use a more modern API call in FileCommit()

- this seems to be a more recent API call and also supports e.g. SMB3,
  ReFS, which is not guaranteed for commit_()
- link to MSDN: http://msdn.microsoft.com/en-us/library/windows/desktop/aa364439%28v=vs.85%29.aspx
Updated fallback seed nodes from sipa's DNS seeds
Add check for valid keys in `importprivkey`

The base58 armoring was checked, but not the resulting private key,
which could be out of range. Fix this by adding a check.
Merge pull request #3593

c7f9332 Add check for valid keys in `importprivkey` (Wladimir J. van der Laan)
Merge pull request #3582

e5aadb2 Updated fallback seed nodes from sipa's DNS seeds (Gavin Andresen)
Re-add newline to error() messages

As reported by @Subo1978, error messages don't have a trailing newline
anymore after commit b77dfdc9. Add back this newline.
Merge pull request #3450

4c0b2cd Win32: use a more modern API call in FileCommit() (Philip Kaufmann)