WL#2915: Caching of Metadata in NDB

Affects: Server-7.1   —   Status: Un-Assigned   —   Priority: Medium

Currently all meta-data is saved in memory in each NDB node.
This WL ensures that not all meta-data need to be in main memory at all
times. Thus when meta-data of a table, index, .. is needed one first checks if
it is in memory at the moment, if not something is thrown out and the meta-data 
is read from disk.