Installer Class missing array variable check

Fixes:
PHP Warning:  substr() expects parameter 1 to be string, array given in /var/www/openemr/library/classes/Installer.class.php on line 311, referer: http://openemr.example.com/setup.php?site=default

Explained in Forum Post:
https://sourceforge.net/p/openemr/discussion/202506/thread/848c1507/
Replaced all "=&$var" with "= &$var" to standardize for later removal of deprecated pass by reference
Missing $_REQUEST variable in messages check

Fixes:
PHP Notice:  Undefined index: form_inactive in /var/www/openemr/interface/main/messages/messages.php on line 65, referer: http://openemr.example.com/interface/main/main_screen.php?auth=login&site=default

Explained in Forum Post:
http://sourceforge.net/p/openemr/discussion/202506/thread/fe1103ea/