some additional tests and fixes around keypathexpr
almost all tests. last case is "reassign" of input in new section
better approach to delegate resolve up to mustache
simplified test case
backport 85fc05d86f91d76de2a0eb364d4606a701f7336b from dev to master as nodeunit tests failing
Merge pull request #611 from ractivejs/resolve-kpexpr

Fixes for resolve keypath expressions. Issue of keypath-mustache reassignment was pre-existing (pretty sure), so divorcing it from these changes