Implement adoptWithCaveats() for struct lists, and some parser tweaks.
.capnp parser WIP
Fix test bug on 32-bit arch.
Continuing work on capnp C++ parser.
Fix pointer corruption when using orphaned struct lists.
Fix file name extension for parser.c++.
Complete C++ .capnp parser.  Also, add a pretty-printing function for arbitrary Cap'n Proto objects which is like the existing stringification but uses whitespace (newlines an indentation) to make the structures more readable.
This should have been in the last commit but apparently I botched the --amend and then pushed without realizing.