Add the non-standard system variables used by the IDL Astronomy Library
Also defines the environment variable ASTRO_DATA pointing to the
directory containing data files associated with the IDL Astronomy
library (system dependent -- user must edit the third line in the
The non-standard system variables !PRIV, !TEXTUNIT, and
!TEXTOUT are added using DEFSYSV.
Written, Wayne Landsman, July 1986.
Use DEFSYSV instead of ADDSYSVAR December 1990
Test for system variable existence before definition July 2001
Assume since V55, remove VMS support W. Landsman Sep 2006
Remove !Debug, comment out ASTRO_DATA definition WL Jan 2009