Problems identified by Coverity in the reftable code have been
corrected.
* hn/reftable-coverity-fixes:
reftable: add print functions to the record types
reftable: make reftable_record a tagged union
reftable: remove outdated file reftable.c
reftable: implement record equality generically
reftable: make reftable-record.h function signatures const correct
reftable: handle null refnames in reftable_ref_record_equal
reftable: drop stray printf in readwrite_test
reftable: order unittests by complexity
reftable: all xxx_free() functions accept NULL arguments
reftable: fix resource warning
reftable: ignore remove() return value in stack_test.c
reftable: check reftable_stack_auto_compact() return value
reftable: fix resource leak blocksource.c
reftable: fix resource leak in block.c error path
reftable: fix OOB stack write in print functions
