Unquoted Constant, Undefined Variables, Index, Initialization - PHP Notices fixed

All from:
referer: http://openemr.example.com/interface/main/left_nav.php

Undefined index: mode in /var/www/openemr/interface/billing/billing_report.php on line 28
Undefined index: mode in /var/www/openemr/interface/billing/billing_report.php on line 54
Undefined index: authorized in /var/www/openemr/interface/billing/billing_report.php on line 71
Use of undefined constant html_header_show - assumed 'html_header_show' in /var/www/openemr/interface/billing/billing_report.php on line 104
Undefined variable: all in /var/www/openemr/library/billrep.inc on line 116
Undefined variable: divnos in /var/www/openemr/interface/billing/billing_report.php on line 1110
Missing Parenthesis fixed