Filecache cleanup.
Filecache cleanup.

Filecache no longer stores file pointers for tracked files, since
the performance benefits are dubious and theoratically, we might
hit an file descriptor limit if we're serving small enough files
on a large enough quota.

Also, cleaned up some code to use 'ioutil' methods instead of 'os'
methods.

deuill/mash,deuill/mash,deuill/mash