add build option debug-disk-pool to log disk buffers allocated by category #2970

Job	Run time
Build (asio-debugging=on picker-debugging=on windows-version=vista)	11m 30s
MingW (address-model=64)	15m 58s
Build (deprecated-functions=off)	11m 24s
Simulations	18m 18s
Test (address-model=32 crypto=built-in)	15m 7s
Test (address-model=64)	15m 3s
Test (release)	18m 9s
	1h 45m 29s

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