Problem:  The error message "does not define the method FIRSTKEY" appears when using both
          Devel::DumpTrace and DB_File at the same time.

This happens within DB_File, even when you just use its own test code.


$ cd /var/tmp/DB_File/
$ wget https://cpan.metacpan.org/authors/id/P/PM/PMQS/DB_File-1.859.tar.gz
$ tar -xvzf DB_File-1.859.tar.gz
$ cd DB_File-1.859/t/
$ perl -d:DumpTrace db-btree.t
>>>>  db-btree.t:36:[__top__]:           print "1..197\n";
1..197
>>>>  db-btree.t:38:[__top__]:           unlink glob "__db.*";
>>>>  db-btree.t:65:[__top__]:               package Redirect ;
>>>>> db-btree.t:125:[__top__]: my $db185mode:'' =  ($DB_File::db_version:5.3 == 1 && ! $DB_File::db_185_compat:0) ;
>>>>> db-btree.t:126:[__top__]: my $null_keys_allowed:1 = ($DB_File::db_ver:5.003021 < 2.004010
>>>>> db-btree.t:129:[__top__]: my $TEMPDIR:'/tmp/1SsBLxMwiy' = tempdir( CLEANUP => 1 );
>>>>  db-btree.t:130:[__top__]:          chdir '/tmp/1SsBLxMwiy';
>>>>> db-btree.t:132:[__top__]: my $Dfile:'dbbtree.tmp' = "dbbtree.tmp";
>>>>  db-btree.t:133:[__top__]:          unlink 'dbbtree.tmp';
>>>>  db-btree.t:135:[__top__]:          umask(0);
DB_File::BTREEINFO does not define the method FIRSTKEY at /usr/local/share/perl5/Devel/DumpTrace.pm line 634.