change cache key

[miurahr]

• change cache key from $scheme$host$request_uri to $http_host$request_uri Users should remove old cache before upgrade tileman.

  ignore difference in schema http/https

  in default configuration cache key might be ex. KEY: openstreetmap_backend/15/2000/3000.png

• add warnig comment for filesystem inode parameter bacause of very small and huge number of cache object will made.
• Now cache will be active in 7days. follows OSM tile policy.

Signed-off-by: Hiroshi Miura miurahr@linux.com