lumiera_error_set() now takes an optional extra string which can be used
to pass context relevant data along. This string gets copied into the
error state so one can easily create it by the tmpbuf_snprintf() facility.
Also a lot of places which define errors get fixed according to this.
* backend.filehandles maximum filehandles used
* backend.mmap_window_size mapping window start size
* backend.as_limit address space limit
This needs to be changed to use the lumieraorg_configuration interface.
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
