make all catch() arguments const

- I saw this on http://en.cppreference.com/w/cpp/language/try_catch and
  thought it would be a good idea
- also unify used format to better be able to search for exception
  uses in our codebase

src/script/bitcoinconsensus.cpp

@@ -79,7 +79,7 @@ int bitcoinconsensus_verify_script(const unsigned char *scriptPubKey, unsigned i
          set_error(err, bitcoinconsensus_ERR_OK);
 
         return VerifyScript(tx.vin[nIn].scriptSig, CScript(scriptPubKey, scriptPubKey + scriptPubKeyLen), flags, SignatureChecker(tx, nIn), NULL);
-    } catch (std::exception &e) {
+    } catch (const std::exception&) {
         return set_error(err, bitcoinconsensus_ERR_TX_DESERIALIZE); // Error deserializing
     }
 }