By Amanda Stephenson and Scott DiSavino (Reuters) -Some natural gas producers in Western Canada are aggressively cutting output in an effort to ease an ongoing glut that this week tipped prices for the fuel into record negative territory, companies and analysts said. Daily spot prices at the Alberta Energy Company (AECO) storage hub averaged minus 5 cents per million British thermal units on Thursday, after trading at record low levels of minus 18 cents this week. The benchmark averaged $1.03 per mmBtu s ...