$common is a hash reference used in every script. It contains one or more of
these scalar items:

cgi
A CGI object from CGI.pm.

config
A hash of configuration parsed from the main Captrap config file.

dbh
A connected database handle from DBI.pm.

priv
Information particular to the containing script.

recur
Hash of information used by the recursive downloading functions.


These elements may not be altered once set--and it shouldn't matter which
script did the setting in the first place. There are two exceptions to this
rule:

1. 'priv' should be considered local to a generation function (mk_views(),
    mk_graph(), etc.) and its decendants. The tree_put() function saves 'priv'
    before recursing and restores it afterward.

2. The 'dbh' database handle will be logged on as a priviliged user if it was
   initialized by one of the administration scripts (sbin/*). Admin scripts and
   unprivileged user scripts should not be mixed anyway.
