[DotGNU]Patches 919 & 920 Add Stubs for SetCreationTime and Impl for Directory.Set*Time

[Aditya P. Bansod]

Hi all,

These are two patches to pnet & pnetlib that add the internal call path for
SetCreationTime (which causes an exception to be thrown, since I can't
really think of a way to set that time on Un*x, or if it's even possible).

Also, this patch implements the Set time methods in the Directory class (by
making calls to FileMethods).

--Aditya