Generates an error if the variable is not a floating point integer.
errmsg=apifun_checkflint(funname,var,varname,ivar)
a 1-by-1 matrix of strings, the name of the calling function.
a matrix of valid Scilab data type, the variable
a 1-by-1 matrix of string, the name of the variable
a 1-by-1 matrix of floating point integers, the index of the input argument in the calling sequence
a 1-by-1 matrix of strings, the error message. If there was no error, the error message is the empty matrix.
Checks that the variable var is a "constant" and that its content is an integer (i.e. the value has no fractional part). This is checked with the condition and(round(x)==x).