Add ability to skip display of submenus
Add check to ensure php fastcgi handler sets SCRIPT_NAME
Tidy require_api/require_lib

1) $t_existing_globals is never used
2) avoid using extract()
3) fix Mantis build on phpng (which currently doesn't define the globals)
Avoid duplicating code: use user_get_all_accessible_projects api
Use report_bug_threshold instead of REPORTER for access control

Following @dregads comment on https://github.com/mantisbt/mantisbt/pull/351

This moves use of REPORTER to config_get() calls
Add admin check to ensure mbstring is loaded.

This ensures that Mantis is running at optimal performance.