implement minimal stratified postinstall

implement minimal stratified postinstall

    	* install.cc (do_install_thread): Remove initialization for
    	run_script.
    	* postinstall.cc (do_postinstall_thread): Remove initialization
    	for run_script.  Implement stratified postinstall (hardcode three
    	strata for now).  For each stratum, run perpetual scripts first
    	after sorting them as ASCII, then the postinstall scripts just
    	installed, then check for dormant scripts in postinstall and try
    	to run those.
    	(PerpetualFindVisitor): New helper class to pick up perpetual
    	scripts.
    	(RunFindVisitor): Use new Script member function and pick up only
    	runnable non-perpetual scripts.
    	* script.h (Script::baseName): Add private variable.
    	(Script::scriptExtension): Ditto.
    	(Script::scriptStratum): Ditto
    	(Script::scriptType): Ditto
    	(Script::allowedStrata): Ditto
    	(Script::allowedTypes): Ditto
    	(Script::match): New private member function.
    	(Script::not_p): New public member function to check for
    	non-perpetual runnable script.
    	(Script::is_p): Ditto, but for perpetual scripts.
    	(Script::operator ==): Qualify as const.
    	(Script::operator <): New const qualified, used for sorting as ASCII.
    	* script.cc (class Script): Implement those additional members.
    	(run): Implement using the new member variables and std::string
    	functions instead of C string manipulations.
    	(isAScript): Ditto.
    	(fullName): Ditto.
    	(baseName): Ditto.
    	(Script): Extend initialization section and calculate values for
    	member variables.  Move initialization for run_script into the constructor.