fix FreeBSD before 7 building, broken in r2616
diff --git a/auto/headers b/auto/headers
index cdd5d29..6f5225f 100644
--- a/auto/headers
+++ b/auto/headers
@@ -6,6 +6,7 @@
 ngx_include="inttypes.h";    . auto/include
 ngx_include="limits.h";      . auto/include
 ngx_include="sys/filio.h";   . auto/include
+ngx_include="sys/param.h";   . auto/include
 ngx_include="sys/mount.h";   . auto/include
 ngx_include="sys/statvfs.h"; . auto/include
 ngx_include="crypt.h";       . auto/include