- added missing quit command to global help topics
- added hint about help [topic]
- let x11runas determine the DISPLAY itself by using MCORE_XORG_DISPLAY
- added no_duplicate() function for internal use
- let require() and provide() check for duplicate items via no_duplicate()
- added verify_requirements to be able to resolve missing plugin requirements
- mecho() and eecho() should honor the '-n' echo option
- added path_not_empty() functions which is used by helper_graphic_rebuild_xorg_conf_d() of the graphic plugin