Perl eval improvements in eg_staged_bib_overlay.

Perl eval improvements in eg_staged_bib_overlay.

Two changes to improve the eval conditions added in the previous
commit:

1. Both error handlers now warn with the same message:

   Record $i is bad: $@; skipping.

Thereby reporting the original message in case the user wants to try
and recover the records later.

2. If a bib record's 901$c is either missing or not numeric, die() is
called with a message to that effect.  This eliminates the Perl
warnings about exiting an eval block with next.

Signed-off-by: Jason Stephenson <jason@sigio.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>