message: Fix comment and remove warning
diff: * \brief Logs an Debug message iff EXP is true
  * \param [in] EXP user-supplied boolean expression.
  * \param [in] msg user-supplied message.
  - * \note The SLIC_DEBUG_IF macro is always active.
  + * \note The SLIC_DEBUG_IF macro is active in debug mode.
  *
  * Usage:
  * \code
  #else // turn off debug macros
  #define SLIC_DEBUG( ignore_EXP ) ( (void)0 )
  -#define SLIC_DEBUG_IF( ignore_EXP, ignore_EXP ) ( (void)0 )
  +#define SLIC_DEBUG_IF( ignore_EXP, ignore_msg ) ( (void)0 )
  #endif
  