FcStrCopyFilename constructs an absolute pathname from
s. It converts any leading '~' characters in
to the value of the HOME environment variable, and any relative paths are
converted to absolute paths using the current working directory. Sequences
of '/' characters are converted to a single '/', and names containing the
current directory '.' or parent directory '..' are correctly reconstructed.
Returns NULL if '~' is the leading character and HOME is unset or disabled
(see FcConfigEnableHome).