Allow Data::Dumper to work on older Perls

Commit 0eb30aebe20a48d634d4e484bc9e6005dffc1420 changed D:D to use the
macro isWORDCHAR instead of isALNUM.  The problem is that this macro is
not defined in older Perls.  This new commit defines isWORDCHAR to be
isALNUM when it isn't already defined, thus avoiding the problem.

Signed-off-by: David Golden <dagolden@cpan.org>