Fix PLIST issue regarding pthread-barrier.h not installed that affects NetBSD
and probably other PLATFORMs as well.

Index: Makefile
===================================================================
RCS file: /cvsroot/pkgsrc/devel/libuv/Makefile,v
retrieving revision 1.9
diff -u -p -r1.9 Makefile
--- Makefile	12 Nov 2016 07:47:34 -0000	1.9
+++ Makefile	13 Nov 2016 11:35:46 -0000
@@ -15,7 +15,7 @@ USE_LIBTOOL=	yes
 USE_TOOLS+=	autoconf automake pkg-config
 GNU_CONFIGURE=	yes
 
-HEADERS=	uv-aix.h uv-bsd.h uv-darwin.h uv-linux.h uv-sunos.h	\
+HEADERS=	pthread-barrier.h uv-aix.h uv-bsd.h uv-darwin.h uv-linux.h uv-sunos.h	\
 		uv-unix.h uv-win.h
 
 pre-configure: