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/bitcoin-cli.cpp

@@ -86,7 +86,7 @@ static bool AppInitRPC(int argc, char* argv[])
     }
     try {
         ReadConfigFile(mapArgs, mapMultiArgs);
-    } catch(std::exception &e) {
+    } catch (const std::exception& e) {
         fprintf(stderr,"Error reading configuration file: %s\n", e.what());
         return false;
     }
@@ -206,7 +206,7 @@ int CommandLineRPC(int argc, char *argv[])
                 // Connection succeeded, no need to retry.
                 break;
             }
-            catch (const CConnectionFailed& e) {
+            catch (const CConnectionFailed&) {
                 if (fWait)
                     MilliSleep(1000);
                 else
@@ -214,10 +214,10 @@ int CommandLineRPC(int argc, char *argv[])
             }
         } while (fWait);
     }
-    catch (boost::thread_interrupted) {
+    catch (const boost::thread_interrupted&) {
         throw;
     }
-    catch (std::exception& e) {
+    catch (const std::exception& e) {
         strPrint = string("error: ") + e.what();
         nRet = EXIT_FAILURE;
     }
@@ -240,7 +240,7 @@ int main(int argc, char* argv[])
         if(!AppInitRPC(argc, argv))
             return EXIT_FAILURE;
     }
-    catch (std::exception& e) {
+    catch (const std::exception& e) {
         PrintExceptionContinue(&e, "AppInitRPC()");
         return EXIT_FAILURE;
     } catch (...) {
@@ -252,7 +252,7 @@ int main(int argc, char* argv[])
     try {
         ret = CommandLineRPC(argc, argv);
     }
-    catch (std::exception& e) {
+    catch (const std::exception& e) {
         PrintExceptionContinue(&e, "CommandLineRPC()");
     } catch (...) {
         PrintExceptionContinue(NULL, "CommandLineRPC()");