Add a benchmark for calling ConnectBlock on a block with many inputs

Requires placing block-107134.tar.gz (containing the block, and a fake CoinsDB
containing its inputs) into the base directory of the repository. This can be
generated using qa/zcash/create_benchmark_archive.py (see the script for usage
details).

To facilitate generation of the fake CoinsDB, an additional field 'valueZat' has
been added to 'getrawtransaction' containing the integer number of zatoshis
instead of a decimal number of ZEC.

Closes #2355.

src/zcbenchmarks.h

@@ -15,5 +15,6 @@ extern double benchmark_verify_equihash();
 extern double benchmark_large_tx();
 extern double benchmark_try_decrypt_notes(size_t nAddrs);
 extern double benchmark_increment_note_witnesses(size_t nTxs);
+extern double benchmark_connectblock_slow();
 
 #endif