pressing TAB after string_var= will insert the current
value of that variable. Note that this works only for
variables of type 'string'.

Also fixes the following buglets in command-completion:

 1. doesnt work if you started the command-line with
 whitespace

 2. Seems to think that 'Set', 'ReSeT', etc are valid
 commands (since it checks for 'strcasecmp' instead of
 'strcmp' when completing the variable names Also fixes
 the following buglets in command-completion:

(From: Vikas Agnihotri <VikasA@att.com>)