Fixed estimated_params_init behaviour...

... when an initial value is given to a parameter that is not
estimated.

The generated driver file was crashing with cryptic error message
because we were searching in the first (and second) column of a
potentially empty array with 0 columns. The fix is to initialize the
fields of estimated_params_ with empty arrays with 10 columns (ie
zeros(0, 10)). Also print a message in the matlab command window if
parameter declared in estimated_params_init is not estimated.