Similarly to deprecating close(), I am now deprecating fclose() and
introduce VIR_FORCE_FCLOSE() and VIR_FCLOSE(). Also, fdopen() is replaced with
VIR_FDOPEN().

Most of the files are opened in read-only mode, so usage of
VIR_FORCE_CLOSE() seemed appropriate. Others that are opened in write
mode already had the fclose()<  0 check and I converted those to
VIR_FCLOSE()<  0.

I did not find occurrences of possible double-closed files on the way.