Unit Tests

- Added proper handling for when no command or filter is specified, and
  no rc.default.command exists.
- Improved wording on above error message.
- Fixed typo in previous commit (managed to check in code before the
  build completed, and ultimately failed).
- Now reports errors that occur during initialization at the same level
  of verbosity as during command execution.

src/Arguments.cpp

@@ -683,7 +683,7 @@ void Arguments::inject_defaults ()
       if (defaultCommand != "")
       {
         capture_first (defaultCommand);
-        context.header ("[task " + trim (defaultCommand) + "]");
+        context.header ("[" + combine () + "]");
       }
       else
         throw std::string (STRING_TRIVIAL_INPUT);