Bug 912795 - make export doesn't handle install/purge manifests. r=gps

At the same time, fix a few things in the top-level Makefile.in.
Bug 912801 - Avoid defining PROGRAM in top-level Makefile. r=gps
Bug 912292 - Fix a few rules relying on being executed after traversing subdirectories. r=gps
Bug 912292 - Always traverse sub-directories after executing rules in the current directory. r=gps
Bug 912845 - Fix typo in js/src/Makefile.in making some headers exported during make libs instead of make export. r=gps
Bug 912846 - Bump pymake parser MRU cache to 50 items. r=gps