Resolve issue bitcoin/bitcoin#3166.

These changes decode valid SIGHASH types on signatures in assembly (asm) representations of scriptSig scripts.
This squashed commit incorporates substantial helpful feedback from jtimon, laanwj, and sipa.

doc/release-notes.md

@@ -19,3 +19,30 @@ For example:
 It is recommended to use this for sensitive information such as private keys, as
 command-line arguments can usually be read from the process table by any user on
 the system.
+
+Asm representations of scriptSig signatures now contain SIGHASH type decodes
+----------------------------------------------------------------------------
+
+The `asm` property of each scriptSig now contains the decoded signature hash
+type for each signature that provides a valid defined hash type.
+
+The following items contain assembly representations of scriptSig signatures
+and are affected by this change:
+
+- RPC `getrawtransaction`
+- RPC `decoderawtransaction`
+- REST `/rest/tx/` (JSON format)
+- REST `/rest/block/` (JSON format when including extended tx details)
+- `zcash-tx -json`
+
+For example, the `scriptSig.asm` property of a transaction input that
+previously showed an assembly representation of:
+
+    304502207fa7a6d1e0ee81132a269ad84e68d695483745cde8b541e3bf630749894e342a022100c1f7ab20e13e22fb95281a870f3dcf38d782e53023ee313d741ad0cfbc0c509001
+
+now shows as:
+
+    304502207fa7a6d1e0ee81132a269ad84e68d695483745cde8b541e3bf630749894e342a022100c1f7ab20e13e22fb95281a870f3dcf38d782e53023ee313d741ad0cfbc0c5090[ALL]
+
+Note that the output of the RPC `decodescript` did not change because it is
+configured specifically to process scriptPubKey and not scriptSig scripts.