script: create sane error return codes for script validation and remove logging

Attempt to codify the possible error statuses associated with script
validation. script/types.h has been created with the expectation that it will
be part of the public lib interface. The other flag enums will be moved here in
a future commit.

Logging has also been removed in order to drop the dependency on core.h. It can
be re-added to bitcoind as-needed. This makes script verification finally free
of application state and boost!

src/script/script_error.cpp

@@ -0,0 +1,67 @@
+// Copyright (c) 2009-2010 Satoshi Nakamoto
+// Copyright (c) 2009-2014 The Bitcoin developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include "script_error.h"
+
+const char* ScriptErrorString(const ScriptError serror)
+{
+    switch (serror)
+    {
+        case SCRIPT_ERR_OK:
+            return "No error";
+        case SCRIPT_ERR_EVAL_FALSE:
+            return "Script evaluated without error but finished with a false/empty top stack element";
+        case SCRIPT_ERR_VERIFY:
+            return "Script failed an OP_VERIFY operation";
+        case SCRIPT_ERR_EQUALVERIFY:
+            return "Script failed an OP_EQUALVERIFY operation";
+        case SCRIPT_ERR_CHECKMULTISIGVERIFY:
+            return "Script failed an OP_CHECKMULTISIGVERIFY operation";
+        case SCRIPT_ERR_CHECKSIGVERIFY:
+            return "Script failed an OP_CHECKSIGVERIFY operation";
+        case SCRIPT_ERR_NUMEQUALVERIFY:
+            return "Script failed an OP_NUMEQUALVERIFY operation";
+        case SCRIPT_ERR_SCRIPT_SIZE:
+            return "Script is too big";
+        case SCRIPT_ERR_PUSH_SIZE:
+            return "Push value size limit exceeded";
+        case SCRIPT_ERR_OP_COUNT:
+            return "Operation limit exceeded";
+        case SCRIPT_ERR_STACK_SIZE:
+            return "Stack size limit exceeded";
+        case SCRIPT_ERR_SIG_COUNT:
+            return "Signature count negative or greater than pubkey count";
+        case SCRIPT_ERR_PUBKEY_COUNT:
+            return "Pubkey count negative or limit exceeded";
+        case SCRIPT_ERR_BAD_OPCODE:
+            return "Opcode missing or not understood";
+        case SCRIPT_ERR_DISABLED_OPCODE:
+            return "Attempted to use a disabled opcode";
+        case SCRIPT_ERR_INVALID_STACK_OPERATION:
+            return "Operation not valid with the current stack size";
+        case SCRIPT_ERR_INVALID_ALTSTACK_OPERATION:
+            return "Operation not valid with the current altstack size";
+        case SCRIPT_ERR_OP_RETURN:
+            return "OP_RETURN was encountered";
+        case SCRIPT_ERR_UNBALANCED_CONDITIONAL:
+            return "Invalid OP_IF construction";
+        case SCRIPT_ERR_SIG_HASHTYPE:
+            return "Signature hash type missing or not understood";
+        case SCRIPT_ERR_SIG_DER:
+            return "Non-canonical DER signature";
+        case SCRIPT_ERR_MINIMALDATA:
+            return "Data push larger than necessary";
+        case SCRIPT_ERR_SIG_PUSHONLY:
+            return "Only non-push operators allowed in signatures";
+        case SCRIPT_ERR_SIG_HIGH_S:
+            return "Non-canonical signature: S value is unnecessarily high";
+        case SCRIPT_ERR_SIG_NULLDUMMY:
+            return "Dummy CHECKMULTISIG argument must be zero";
+        case SCRIPT_ERR_UNKNOWN_ERROR:
+        case SCRIPT_ERR_ERROR_COUNT:
+        default: break;
+    }
+    return "unknown error";
+}