This patch fixes the following bugs in the Bug Tracker:

[ 1325071 ] "as" keyword sometimes highlighted in strings


This patch fixes the following undocumented bugs:

* "as" keyword colored as a keyword even in comments on
the 'import' line
* Comments such as "#False identity", which start with
a keyword immediatly after the '#' character, aren't
colored as comments.
* In unicode string literals (e.g. u"bob"), the
preceding 'u' character isn't colored as part of the
string. But the preceding 'r' of raw string literals is.

I have only added/fixed minor details, no logic changes.