change __colset__ function on composite types

[Mike Bayer]

xoraxax tells me __colset__ conflicts with something in python.

[jek]

if this is addressed, {{{emulates}}} and {{{instruments}}} in collections should be changed as well

[jek]

dodged the issue in aac6598ecc400f9b3a8d69fae88e6882b9e7b597 with the rename to composite_values, the internal underscore effectively makes this a namespaced magic name.

emulates and friends are still an open question and should get a new ticket if they're to be changed.

[Mike Bayer]

Removing milestone: 0.4.0 (automated comment)