Beta version 1.6.6.a

NOTE: Do not use this beta version unless you are asked to test it.

Bugfixes:

• Issue with internal tree node names changed from slash to underscore (reported by JP Flandrois).
• ASSERT with protein mixture models (reported by Giddy Landan).
• Disallow specifying both --runs with -lmap option (reported by Giap Nguyen)
• Reading nexus composite characters for non-DNA data (reported by a web user)
• Support amino-acid O (22nd amino-acid), which is regarded as missing data (reported by Cuong).
• Initialising free-rate model, which may create negative rates in rare cases (reported by Paul Frandsen).