In the case where the allocated buffer is not large enough to hold
the resulting absolute path, we were writing out a null terminator
outside of the buffer, instead of at its beginning.

Also fixes potential issue where split_path would not initialize
the count to zero if it returned a failure.

Fixes: #81

* Do not segfault on passing NULL path to get_{dir,base}name
* There is no way dirname can return "..", remove that code
* Buffer overflow in path_concat
* Expand . in get_basename
* Return NULL rather than crash in split_path on passing NULL path
* Be more defensive in directory_list

Additional changes.

This patch replaces int with int32_t,
unsigned with uint32_t, long with int64_t,
unsigned long with uint64_t as values
that collection can store and hold.