WUtil: fixed possible problem in wcopy_file (Coverity #50141)
As pointed by Coverity, the macro RETRY does not behave as expected, as it
assumes that errno is cleared on successful 'fopen' call which is not the
case.
This patch removes the uses of the macro RETRY:
- fopen: with the appropriate check
- fread/fwrite: nothing because they do not set errno
- fclose: nothing because retrying is not recommended
and took the opportunity to add a little bit more information in the error
messages.
Signed-off-by: Christophe CURIS <christophe.curis@free.fr>