Declare single-argument (non-converting) constructors "explicit"

In order to avoid unintended implicit conversions.

src/script/interpreter.h

@@ -114,7 +114,7 @@ struct PrecomputedTransactionData
 {
     uint256 hashPrevouts, hashSequence, hashOutputs;
 
-    PrecomputedTransactionData(const CTransaction& tx);
+    explicit PrecomputedTransactionData(const CTransaction& tx);
 };
 
 enum SigVersion

src/script/sign.h

@@ -21,7 +21,7 @@ protected:
     const CKeyStore* keystore;
 
 public:
-    BaseSignatureCreator(const CKeyStore* keystoreIn) : keystore(keystoreIn) {}
+    explicit BaseSignatureCreator(const CKeyStore* keystoreIn) : keystore(keystoreIn) {}
     const CKeyStore& KeyStore() const { return *keystore; };
     virtual ~BaseSignatureCreator() {}
     virtual const BaseSignatureChecker& Checker() const =0;
@@ -54,7 +54,7 @@ public:
 /** A signature creator that just produces 72-byte empty signatures. */
 class DummySignatureCreator : public BaseSignatureCreator {
 public:
-    DummySignatureCreator(const CKeyStore* keystoreIn) : BaseSignatureCreator(keystoreIn) {}
+    explicit DummySignatureCreator(const CKeyStore* keystoreIn) : BaseSignatureCreator(keystoreIn) {}
     const BaseSignatureChecker& Checker() const override;
     bool CreateSig(std::vector<unsigned char>& vchSig, const CKeyID& keyid, const CScript& scriptCode, SigVersion sigversion) const override;
 };

src/script/standard.cpp

@@ -253,7 +253,7 @@ class CScriptVisitor : public boost::static_visitor<bool>
 private:
     CScript *script;
 public:
-    CScriptVisitor(CScript *scriptin) { script = scriptin; }
+    explicit CScriptVisitor(CScript *scriptin) { script = scriptin; }
 
     bool operator()(const CNoDestination &dest) const {
         script->clear();