[gradsusr] Request environment variable for shapefiles

[Dave Allured]

Hi.  This is a feature request for a separate environment variable 
for the path to shapefiles.  In recent GrADS versions, GADDIR is 
used for both installation data files and shapefiles.  Mixing an 
installation directory with a user supplemented directory can create 
some problems.

I think a new environment variable such as GASHAPEDIR would be most 
helpful.  It would be nice if multiple paths could be specified as a 
space separated list, as is now the case for GASCRP.  For 
compatibility, I suggest that the search order for shapefiles be as 
follows:

1.  Current directory.
2.  Paths in GASHAPEDIR, left to right.
3.  GADDIR.

There are other ways to accomplish the goal.  Multiple paths in 
GADDIR is one of them.  A separate environment variable seems most 
user friendly to me.

If desired, I would be willing to attempt a patch for this.  What do 
you think?

--Dave A.
NOAA/PSD/CIRES
Boulder, Colorado