Update: f_path related improvements.

Update: f_path related improvements.

Return F_data_not rather than F_false to provide a more detailed reason as to the return status of f_path_is().

Explicitly check fo F_true when calling f_path_is() because it now returns F_data_not without the error bit.

Add f_path_is_relative().
Pretty much every path that does not begin with a "/" is a relative path.
This function performs a dirt simple check to achieve this.
This function does not perform any checks to see if the path would be a valid path.
Such decisions are filesystem and are otherwise too situation dependent to be reliable detect in a general manner.

Use f_path_separator_s rather than an explicit "/".

Simplify counter using a pre-increment within the if condition check.