Resolves a relative path for
file to an absolute path.
This call does no blocking I/O.
relative_path is an absolute path name, the resolution
is done absolutely (without taking
file path as base).
A given relative path string.
|The data is owned by the caller of the function.|
|The value is a file system path, using the OS encoding.|
|The caller of the method takes ownership of the data, and is responsible for freeing it.|