fileErrorFromErrno
Gets a #GFileError constant based on the passed-in @err_no.
For example, if you pass in EEXIST this function returns %G_FILE_ERROR_EXIST. Unlike errno values, you can portably assume that all #GFileError values will exist.
Normally a #GFileError value goes into a #GError returned from a function that manipulates files. So you would use g_file_error_from_errno() when constructing a #GError.
Return
#GFileError corresponding to the given @err_no
Parameters
errNo
an "errno" value