We will need cluster/page aligned access for certain files (indices),
this files will contain an initial header describing the contents. A bias
is used to step over this header and align the following data.
Quite some code which was hold back in favor of the config and plugin stuff
implements:
* mmapcache: mru cache for unused memory mappings
* mmap: single mmaped areas
* mmapings: manages mmaps established for one filedescriptor
