-Add the hashtable.h and sarray.h files from net3-base.

git-svn-id: http://odamex.net/svn/root/trunk@4215 b0bcef46-2027-0410-bd56-ab726e9a1d04
-Add the clear() member to OString.
-Remove an unnecessary #include from hashtable.h.

git-svn-id: http://odamex.net/svn/root/trunk@4217 b0bcef46-2027-0410-bd56-ab726e9a1d04