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/miner.cpp

@@ -565,7 +565,7 @@ void static BitcoinMiner(CWallet *pwallet)
             }
         }
     }
-    catch (boost::thread_interrupted)
+    catch (const boost::thread_interrupted&)
     {
         LogPrintf("BitcoinMiner terminated\n");
         throw;