[shell] ensure add-col shell is properly quoted #2415

Thanks @frosencrantz for suggestion of fix.

dev/checklists/manual-tests.md

@@ -95,3 +95,4 @@
 23. That DirSheet requires a commit-sheet before changes on filesystem
 24. Test adding multiple aggregators via palette (+)
 25. time vd -p tests/quit-nosave.vdj  - note down the time. compare to PR #2369
+26. Use the z; command. Then type in a command line like echo "| Ceci n'est pas une pipe"

visidata/shell.py

@@ -79,7 +79,7 @@ def calcValue(self, row):
                 else:
                     args.append(arg)
 
-            p = subprocess.Popen([os.getenv('SHELL', 'bash'), '-c', ' '.join(args)],
+            p = subprocess.Popen([os.getenv('SHELL', 'bash'), '-c', shlex.join(args)],
                     stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
             return p.communicate()
         except Exception as e: