Install man pages with correct permissions mask.

doc/manpages/Makefile

@@ -2,6 +2,6 @@ include ../../mconfig
 
 install:
 	mkdir -p "$(DESTDIR)$(MANDIR)/man8"
-	install dinit.8 dinitctl.8 "$(DESTDIR)$(MANDIR)/man8"
+	install -m644 dinit.8 dinitctl.8 "$(DESTDIR)$(MANDIR)/man8"
 	mkdir -p "$(DESTDIR)$(MANDIR)/man5"
-	install dinit-service.5 "$(DESTDIR)$(MANDIR)/man5"
+	install -m644 dinit-service.5 "$(DESTDIR)$(MANDIR)/man5"