Merge branch 'rs/reftable-realloc-errors'

The custom allocator code in the reftable library did not handle
failing realloc() very well, which has been addressed.

* rs/reftable-realloc-errors:
  t-reftable-merged: handle realloc errors
  reftable: handle realloc error in parse_names()
  reftable: fix allocation count on realloc error
  reftable: avoid leaks on realloc error