FIXED:  [case: travel time < 0]
ADDED: comment making
CHANGED: database schema for flightComment.
ADDED: a ...buggy comment search
changed:comment_history
Merge branch 'master' into liang

Conflicts:
	template/.DS_Store
	template/manage/flight.html
	template/manage/flight/flight.html
	template/trade/booking_history.html
	ymmbooking.py
UPDATED: a better flight.html
Merge branch 'zlk'

Conflicts:
	template/manage/flight/flight.html
FIXED: search::order_type, booking_history,comment_histroy,time.
Merge branch 'master' into liang
FIXED: booking_history search.