- support DESTDIR
- preserve timestamp of pstream.h

diff -up pstreams-0.6.0/Makefile.destdir_timestamp pstreams-0.6.0/Makefile
--- pstreams-0.6.0/Makefile.destdir_timestamp	2008-11-07 13:49:44.000000000 +0100
+++ pstreams-0.6.0/Makefile	2008-11-07 13:50:19.000000000 +0100
@@ -77,8 +77,8 @@ clean:
 	@rm -rf doc TODO
 
 install:
-	@install -d $(INSTALL_PREFIX)/include/pstreams
-	@install -v -m0644 pstream.h $(INSTALL_PREFIX)/include/pstreams
+	@install -d $(DESTDIR)$(INSTALL_PREFIX)/include/pstreams
+	@install -p -v -m0644 pstream.h $(DESTDIR)$(INSTALL_PREFIX)/include/pstreams
 
 .PHONY: TODO test ChangeLog