Bug in command line completion

[Rik]

The Mercurial tip for Octave shows an odd behavior for undefined
variables or functions.  Specifically, after attempting to use an
undefined variable it is added to the command line completion list even
though it does not exist.  This behavior is not present in the 3.0.0
stable release.

To reproduce:
1) type 'fo<TAB><TAB>' to show functions and variables starting with 'fo'.
Octave responds with:
fopen    for      fork     format   formula

2) type 'foobar<ENTER>'
Octave responds with:
error: `foobar' undefined near line 1 column 1

3) type 'fo<TAB><TAB>'
Octave responds with:
foobar   fopen    for      fork     format   formula

'foobar' does not appear to be in any other symbol table as the
functions 'who' and 'which' know nothing about foobar.

--Rik