I have re-added the compose/decompose API to the Typekit classes, keeping it
100% compatible with RTT 1.x. Concretely, this means that you implement
composeTypeImpl() and decomposeTypeImpl() by just copy-pasting these functions
from your RTT 1.x toolkit. The semantics have broadend slightly to also allow
non-propertybag conversions, but in that case, you need to override
composeType()/decomposeType() (rare use case). You can use this method for
TemplateTypeInfo, StructTypeInfo, SequenceTypeInfo etc.

I have updated the docs (rtt/doc/xml/orocos-typekit-plugin.xml) to explain
when you need to implement these functions and when not.

For (automated) testing purposes, you can just check that:

typeinfo->composeType( typeinfo->decomposeType( input ), output)
assert( input->get() == output->get() )

where input and output are data sources of same type as 'typeinfo'. Since the
RTT itself does not have such a type, we need some testing/feedback from real
typekits.

This change is supposed to be backwards compatible with 2.0/2.1 typekits as
well (so you're not forced to upgrade to these functions in case you found
another way by now).

I apologize for the pain every 2.x typekit writer has suffered because of the
removal of these two functions. I hope future migrations will be less painful.

Peter