cli: add a tab_pretty() function to a cli command interface

allows commands to specify a delimiter between tab completion
suggestions, the default is '\t' in case this function is not present
in the command interface.

console/autocomplete.js

@@ -10,7 +10,11 @@ function write_suggestions(arr, command)
         write_string(suggestion);
         
         if (i != arr.length-1) {
-            write_char('\t');
+            var ch = '\t';
+            if ((command != undefined) && (command.tab_delim)) {
+                ch = command.tab_delim();
+            }
+            write_char(ch);
         }
     }
     write_char('\n');

documentation/cli.txt

@@ -97,7 +97,11 @@ tab_pretty(arg)
                 used by commands to prettify their autocompletion output, 
                 used by the cd command
 
+tab_delim()     allows commands to specify a delimiter between tab completion 
+                suggestions, the default is '\t' in case this function is not present
+                in the command interface.
+
 help()          should print a helpful description for the command, called when 
                 the user execute "help cmd"
 
-
+a