title: C#: Check if a file is not locked and writable
body: <p>I want to check if a list of files is in use or not writable before I start replacing files.
  Sure I know that the time from the file-check and the file-copy there is a chance that one or more files is gonna to be locked by someone else but i handle those exceptions. I want to run this test before file copy because the complete list of files have a better chance to succeed than if a file in the middle of the operation fails to be replaced.</p>
  
  <p>Have any of you an example or a hint in the right direction</p>