Add blast parameters to BlastMapping constructor

[GoogleCodeExporter]

Now that blast is provided using a class interface, it would make sense to
make the constructor accept blast parameters and the optional al argument.
 Then you wouldn't have to pass those parameters to every method call for
that BlastMapping; this would also allow users to customize the parameters
used by the __getitem__ interface, which currently isn't possible.

Original issue reported on code.google.com by cjlee...@gmail.com on 31 Aug 2009 at 9:31