Resolve #58: Illegal parameter value and unit test

Jan Breuer

2015-10-14 b7e9d6858699f5ea9a23ecf6587e98e7b0e1bc28

 libscpi/inc/scpi/expression.h

@@ -41,7 +41,7 @@
#ifdef __cplusplus
extern "C" {
#endif
    

    enum _scpi_expr_result_t {
        SCPI_EXPR_OK = 0,
        SCPI_EXPR_ERROR,