Changed default alignment to 16.

This fixes alignment problems observerd on ARMs, and likely also needed
for MIPSes.  Unless we know alignment is not required just assume we
need 16, which appears to be safe default for all architectures.

See here for details:
http://mailman.nginx.org/pipermail/nginx/2012-June/034139.html

auto/os/conf

@@ -93,6 +93,7 @@ case "$NGX_MACHINE" in
     ;;
 
     *)
+        have=NGX_ALIGNMENT value=16 . auto/define
         NGX_MACH_CACHE_LINE=32
     ;;