Add alternate signal stack to docs

* new-features.xml (ov-new2.1): Add alterante signal stack info.
	* posix.xml (std-susv4): Move sigaltstack here.

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

winsup/cygwin/release/2.1.0

@@ -1,6 +1,12 @@
 What's new:
 -----------
 
+- First cut of an implementation to allow signal handlers running on an
+  alternate signal stack.
+  
+- New API sigaltstack, plus definitions for SA_ONSTACK, SS_ONSTACK, SS_DISABLE,
+  MINSIGSTKSZ, SIGSTKSZ.
+
 - New API: sethostname.
 
 

winsup/doc/new-features.xml

@@ -8,6 +8,16 @@
 
 <itemizedlist mark="bullet">
 
+<listitem><para>
+First cut of an implementation to allow signal handlers running on an
+alternate signal stack. 
+</para></listitem>
+
+<listitem><para>
+New API sigaltstack, plus definitions for SA_ONSTACK, SS_ONSTACK,
+SS_DISABLE, MINSIGSTKSZ, SIGSTKSZ.
+</para></listitem>
+
 <listitem><para>
 New API: sethostname.
 </para></listitem>

winsup/doc/posix.xml

@@ -763,6 +763,7 @@ also IEEE Std 1003.1-2008 (POSIX.1-2008).</para>
     shutdown
     sigaction
     sigaddset
+    sigaltstack
     sigdelset
     sigemptyset
     sigfillset
@@ -1490,7 +1491,6 @@ also IEEE Std 1003.1-2008 (POSIX.1-2008).</para>
     scalblnl
     scalbnl
     setnetent
-    sigaltstack
     sigtimedwait
     sinhl
     sinl