Remove gc from '_deps' since it is replaced by bdwgc
Fix passenger installation for Pasenger4(.0.5)

.cpl/errors:
  Documente passenger compilation and installation errors
.cpl/params/passenger:
  Now calls a script
.cpl/scripts/pre_passenger:
  Add local include and library path for better library detection
gitlab/apache.cnf.tpl:
  Uses the new 'PassengerEnabled On' directive.