[with patch, positive review] linear codes list function is slow

[rlm]

Before:

sage: G = ExtendedBinaryGolayCode()
sage: time L = G.list()
CPU times: user 16.24 s, sys: 0.32 s, total: 16.57 s
Wall time: 17.14 s

After:

sage: G = ExtendedBinaryGolayCode()
sage: time L = G.list()
CPU times: user 3.65 s, sys: 0.04 s, total: 3.68 s
Wall time: 3.71 s

[rlm]

This may actually be a bugfix, see:  http://trac.sagemath.org/sage_trac/ticket/4115#comment:13

[wdj]

This is obviously correct (the code is 1 line). I didn't know about the list method for vector spaces but I'd not surprised that that list method is a great deal faster and more efficient that the current LinearCodes? one.

I have tested this does fix the comment 13 in #4115. Thanks Robert!

[mabshoff]

Merged in Sage 3.1.3.alpha0