ccache not loading or storing cache files

I've noticed that there is nothing in my /tmp/luci-modulecache
directory. Digging into it it looks like because both the expected uid
and mode of the files doesn't match, so for security reasons they're
long being loaded or saved by ccache.lua (from the luci-lib-core
package). I'm not sure how far back this has been broken but I it
appears to have been quite some time, possibly years?

I've included a patch which updates the checks to use the right newer
function name / structure name. It decreases page load times by about
10-15% on my bcm2708 (raspberrypi). I can create a ticket if you'd
prefer. The patch is against the luci-0.11 branch but should apply to
trunk as well.

Signed-off-by: Bryan Mayland <bmayland@leoninedev.com>