Respect verbosity settings when generating manual pages

docs/man/Makefile.am

@@ -19,8 +19,12 @@ SUBST_VARS = sed \
    -e 's|@localstatedir[@]|$(localstatedir)|g' \
    -e 's|@sysconfdir[@]|$(sysconfdir)|g'
 
+subst_verbose = $(subst_verbose_@AM_V@)
+subst_verbose_ = $(subst_verbose_@AM_DEFAULT_V@)
+subst_verbose_0 = @echo "  SUBST    $@";
+
 SUFFIXES = .in
 .in:
-	$(SUBST_VARS) $< > $@
+	$(subst_verbose)$(SUBST_VARS) $< > $@
 
 CLEANFILES = $(man_MANS)