Bugfix: Problems in f_file functions exposed by unit tests.

Bugfix: Problems in f_file functions exposed by unit tests.

Clean up f_file_name_base() and f_file_name_directory() code.

Use f_string_ascii_period_s rather than f_string_ascii_plus_s to match a period!
Perform this comparison check after allocating the necessary space to ensure a NULL terminated string is returned.

The POSIX standard designates that read() returns 0 on EOF.
Rather than checking for size_read == file.size_read (and similar), check fo size_read to be 0.

When total is 0, return F_data_not for f_file_read_until().