Fix 'make dist' on FreeBSD due to 'cp -r' following symlinks.

cp(1) -r follows symlinks on FreeBSD. POSIX allows -r to be
implementation-defined, while clearly defining -R to do what
I want and expect.

Makefile.in

@@ -103,7 +103,7 @@ distclean: clean
 distrib: clean
 	@rm -rf $(DISTRIB)/
 	-+@cd lib && $(MAKE) distclean
-	@mkdir $(DISTRIB) && cp -r $(DISTROFILES) $(DISTRIB)
+	@mkdir $(DISTRIB) && cp -R $(DISTROFILES) $(DISTRIB)
 	@rm -rf `find $(DISTRIB)/ \( -name '*~' -o -name '*#' -o -name '*.orig' -o -name '*.rej' -o -name '*.bak' -o -name '.gitignore' -o -name '.*.swp' \) -type f -print`
 	@rm -rf `find $(DISTRIB)/ \( -name '.git' -o -name '.deps' \) -type d -print`
 	@for s in $(EXCLUDES); do \