Add support for GLJPATH, remove GLOJURE_STDLIB_PATH

[ingydotnet]

Works for general use and for AOT.

$ (for f in a/a.glj b/b.glj x.glj; do (set -x; cat $f); done)
+ cat a/a.glj
(ns a)
(println "aaa")
+ cat b/b.glj
(ns b)
(println "bbb")
+ cat x.glj
(require 'a)
(require 'b)
(println "xxx")
$ GLJPATH=a:b ./bin/linux_amd64/glj x.glj 
aaa
bbb
xxx
$