add support for python 3 to genshi.template expression evaluator: * add support for python 3 AST: * AST for raise has changed in Python 3. * Python 3 adds AST nodes for individual arguments and Bytes. * use genshi.compat functions for dealing with code objects. * do not coerce byte strings to unicode in Python 3 ASTTransformer. * replace doctests that reply on exception names with uglier but more compatible try:.. except:.. doctest * handle filename preferences of Python 2 and 3 (2 prefers bytes, 3 prefers unicode). * ifilter is gone from itertools in Python 3 so use repeat for tests instead.