Add sethostname

* net.cc (sethostname): New function.
	* common.din (sethostname): Export
	* include/cygwin/version.h (CYGWIN_VERSION_DLL_MAJOR): Bump to 2001.
	(CYGWIN_VERSION_DLL_MINOR): Set to 0.

	* new-features.xml (ov-new): Rename from ov-new1.7.
	(ov-new2.1): Add new section.  Document sethostname.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

winsup/cygwin/release/2.1.0

@@ -0,0 +1,18 @@
+What's new:
+-----------
+
+- New API: sethostname.
+
+
+What changed:
+-------------
+
+
+Bug Fixes
+---------
+
+- Enable non-SA_RESTART behaviour on threads other than main thread.
+  Addresses: https://cygwin.com/ml/cygwin/2015-06/msg00260.html
+
+- Try to handle concurrent close on socket more gracefully
+  Addresses: https://cygwin.com/ml/cygwin/2015-06/msg00235.html