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.h

@@ -0,0 +1,53 @@
+// 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.
+
+#ifndef BITCOIN_SCRIPT_ERROR_H
+#define BITCOIN_SCRIPT_ERROR_H
+
+typedef enum ScriptError_t
+{
+    SCRIPT_ERR_OK = 0,
+    SCRIPT_ERR_UNKNOWN_ERROR,
+    SCRIPT_ERR_EVAL_FALSE,
+    SCRIPT_ERR_OP_RETURN,
+
+    /* Max sizes */
+    SCRIPT_ERR_SCRIPT_SIZE,
+    SCRIPT_ERR_PUSH_SIZE,
+    SCRIPT_ERR_OP_COUNT,
+    SCRIPT_ERR_STACK_SIZE,
+    SCRIPT_ERR_SIG_COUNT,
+    SCRIPT_ERR_PUBKEY_COUNT,
+
+    /* Failed verify operations */
+    SCRIPT_ERR_VERIFY,
+    SCRIPT_ERR_EQUALVERIFY,
+    SCRIPT_ERR_CHECKMULTISIGVERIFY,
+    SCRIPT_ERR_CHECKSIGVERIFY,
+    SCRIPT_ERR_NUMEQUALVERIFY,
+
+    /* Logical/Format/Canonical errors */
+    SCRIPT_ERR_BAD_OPCODE,
+    SCRIPT_ERR_DISABLED_OPCODE,
+    SCRIPT_ERR_INVALID_STACK_OPERATION,
+    SCRIPT_ERR_INVALID_ALTSTACK_OPERATION,
+    SCRIPT_ERR_UNBALANCED_CONDITIONAL,
+
+    /* BIP62 */
+    SCRIPT_ERR_SIG_HASHTYPE,
+    SCRIPT_ERR_SIG_DER,
+    SCRIPT_ERR_MINIMALDATA,
+    SCRIPT_ERR_SIG_PUSHONLY,
+    SCRIPT_ERR_SIG_HIGH_S,
+    SCRIPT_ERR_SIG_NULLDUMMY,
+
+    SCRIPT_ERR_ERROR_COUNT
+} ScriptError;
+
+#define SCRIPT_ERR_LAST SCRIPT_ERR_ERROR_COUNT
+
+const char* ScriptErrorString(const ScriptError error);
+
+#endif // BITCOIN_SCRIPT_ERROR_H