HPCC-9489 Add support to roxie for a checking memory allocator

Can be enabled per-query using @debugHeap, or globally via control:debugHeap
or adding debugHeap=true in the config file.

Note - this is deliberately NOT exposed in configmrg - it's not something
people should enable unless specially instructed.

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>