QDL stack trace has extra line feeds

[jjg-123]

When a QDL script fails, a stack trace of calling scripts is displayed. This has extra line feeds making it hard to read. Also, reverse the order of the scripts, so most recent is first.

[jjg-123]

improved message as well. A stack trace in QDL now looks like

variable 'rsa' not found at (8, 15) in:
/tmp/a2.qdl called at (12,12) in
 /tmp/a1.qdl called at (17,29) in
  /tmp/a0.qdl called at (1,12) in
   /tmp/a.qdl called at (2,19) in
    main

where each line refers to the next.