Now ttail is able to sort logfiles given as arguement.
The sort function _ttail_file_sort place files with no valid date to the
end of the file list and is able to detect if some files overlaps.

No tests written...

Four macros were added :
 - TTAIL_CHECK_START(char *test_suite_str, char *test_case_str)
 - TTAIL_SET_FIXTURE(void (*setup)(), void (*teardown)())
 - TTAIL_ADD_TEST( libcheck_test test)
 - TTAIL_CHECK_END