better check for nodejs in minify.sh and some fixes for enyo.load()

this pull fixes some problems with enyo.load() and minify.sh in 2.4.0:

*loading of multiple files/packages at once: enyo.load(["a","b","c"])
*not working after loading error because enyo.runtimeLoading will be not set back to 'false'
*there is no node on my system, but nodejs

remaining problem is loading of multiple packages like this: enyo.load("a"); enyo.load("b"); enyo.load("c"), which was working in the past. the reason may be building of wrong prefix, saved in enyo.loader.packageFolder. using of such as global variable for this purpose is not good at all