vms stat patches (take 2)

vms stat patches (take 2)

Conversion of Perl_flex_stat_int() to tolerate a null thread context,
and updates to better handle Unix Format or Extended File System
character sets.

vms_fid_to_name() now understands stat/lstat for properly handling
symbolic links, and uses a similar algorithm as Perl_flex_stat_int() for
consistency.  Will now optionally return the mode bits from the stat
operation.

(The parts of the patch that worked around null thread context when
checking vmsish hints are omitted since that's been handled somewhat
differently by a520a2c43dd549df0ebed1f073e13cc4564380db).

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