add build option debug-disk-pool to log disk buffers allocated by category #2971

Job	Run time
Build (asio-debugging=on picker-debugging=on windows-version=vista)	11m 53s
Build (deprecated-functions=off)	10m 55s
MingW (address-model=64)	15m 36s
Simulations	18m 28s
Test (address-model=32 crypto=built-in)	14m 26s
Test (address-model=64)	14m 4s
Test (release)	17m 9s
	1h 42m 31s

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