A define repeated with combine="choice" or combine="interleave" now
merges with the existing definition (as a choice or interleave pattern)
instead of the last one silently replacing it. A plain redefinition with
no combine still replaces. Applied consistently in a grammar and across
include merges.
<param> facets under <data>, datatypeLibrary resolution, typed <value>
comparison, and the RNC-syntax gaps remain.
Part of #79
Mihaela Mihaljevic
24a862e3a0