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.

src/script/interpreter.cpp

@@ -186,7 +186,7 @@ bool static IsDefinedHashtypeSignature(const valtype &vchSig) {
     return true;
 }
 
-bool static CheckSignatureEncoding(const valtype &vchSig, unsigned int flags, ScriptError* serror) {
+bool CheckSignatureEncoding(const vector<unsigned char> &vchSig, unsigned int flags, ScriptError* serror) {
     // Empty signature. Not strictly DER encoded, but allowed to provide a
     // compact way to provide an invalid signature for use with CHECK(MULTI)SIG
     if (vchSig.size() == 0) {

src/script/interpreter.h

@@ -88,6 +88,8 @@ enum
     SCRIPT_VERIFY_CHECKLOCKTIMEVERIFY = (1U << 9),
 };
 
+bool CheckSignatureEncoding(const std::vector<unsigned char> &vchSig, unsigned int flags, ScriptError* serror);
+
 struct PrecomputedTransactionData
 {
     uint256 hashPrevouts, hashSequence, hashOutputs, hashJoinSplits;

src/script/script.cpp

@@ -8,16 +8,6 @@
 #include "tinyformat.h"
 #include "utilstrencodings.h"
 
-namespace {
-inline std::string ValueString(const std::vector<unsigned char>& vch)
-{
-    if (vch.size() <= 4)
-        return strprintf("%d", CScriptNum(vch, false).getint());
-    else
-        return HexStr(vch);
-}
-} // anon namespace
-
 using namespace std;
 
 const char* GetOpName(opcodetype opcode)
@@ -237,26 +227,3 @@ bool CScript::IsPushOnly() const
     }
     return true;
 }
-
-std::string CScript::ToString() const
-{
-    std::string str;
-    opcodetype opcode;
-    std::vector<unsigned char> vch;
-    const_iterator pc = begin();
-    while (pc < end())
-    {
-        if (!str.empty())
-            str += " ";
-        if (!GetOp(pc, opcode, vch))
-        {
-            str += "[error]";
-            return str;
-        }
-        if (0 <= opcode && opcode <= OP_PUSHDATA4)
-            str += ValueString(vch);
-        else
-            str += GetOpName(opcode);
-    }
-    return str;
-}

src/script/script.h

@@ -576,7 +576,6 @@ public:
         return (size() > 0 && *begin() == OP_RETURN) || (size() > MAX_SCRIPT_SIZE);
     }
 
-    std::string ToString() const;
     void clear()
     {
         // The default std::vector::clear() does not release memory.