Correct typo in Biopython 1.64 release date
Use the same code path for SeqUtils.molecular_weigth and ProtParam.molecular_weight

Previously depending on which of these you used, you could get different molecular weights.

Signed-off-by: Kai Blin <kai@samba.org>
Phylo: make default Newick branch length None like the other Clade subclasses.

Fixes Issue #335
Tutorial: updated a Phylo example to match the previous Newick change.

Now test_Tutorial passes too.
Tutorial: enabled doctest for Issue #335 ; updated opuntia Clustal outputs
Add tox.ini info to documentation (suggested by @msabramo)

Original issue: #50
Tests: remove now-superfluous 1.0 branch lengths from TreeConstruction reference
Merge branch 'master' of github.com:biopython/biopython