the buildsystem will now pick up and link
all test cases according to the layer, e.g.
backend tests will automatically be linked
against the backend + library solely.
This adds global exclusive advisory file locks on a per-thread basis.
Only exclusive locking for a whole file is supported to setup headers etc.
Finer grained locking will be handled somewhere else.
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
* add 'backend' for backend global initialization/destruction
and common functions.
* WIP: 'file' acts as interface to named files, provides posix
filehandles with and acquire/release function pair.
* 'filehandle' manages posix filehandles internally, refcounted.
* WIP: 'filehandlecache' keeps unused filehandles in a MRU cache
* WIP: test for filehandle management
* improved filedescriptor test
