gom: Remove "adapter" property from GomResourceGroup

It wasn't used that much, and duplicated what we could have gotten
from GomRepository anyway.
build: Add warning CFLAGS
gom: Fix thinko in is_new_in_version()

Don't really want to be doing arithmetic on a pointer.
gom: Fix a number of build warnings
tests: Fix build warnings

Unused variables and missing declarations.
tests: Fix stress test when upping NUM_RECORDS