Group Indexing operations can be multithreaded

[simonp]

According to the type of database in use, group indexing operations can be sped up significantly by using multiple threads (particularly Batch Import eg. 20000 records loads in approx 1200 seconds single threaded, but in approx 400 seconds with four threads).

Number of threads that can be safely used could be config'd or taken from number of processors available to JVM

Multithreaded behaviour switched off if database should not be used/does not support multiple threads (eg. Mckoi).

[simonp]

Patch to be forthcoming.

[simonp]

Added in svn rev 8114