[docs] python 2.6 does support 'b' prefix on strings

[Pádraig Brady]

In the language reference, there is no mention of the b prefix for string literals.
http://docs.python.org/release/2.6/reference/lexical_analysis.html#literals
This should be added to be consistent with the info here:
http://docs.python.org/release/2.6/whatsnew/2.6.html#pep-3112-byte-literals

The top link should also be adjusted for 2.6.[1-7]

cheers,
Pádraig.