* filer: skip COLLATE "C" list fallback on CockroachDB
CockroachDB string comparison is already byte-ordered, so wrapping the
list queries in COLLATE "C" can never change result order. It reports
datcollate=en_US.utf8 regardless of how the database was created, so the
collation check always misfires and forces the fallback. On 22.1 and
older COLLATE "C" is rejected as an invalid locale, turning every filer
list query into a hard failure. Detect the backend via version() and
keep the default ordering.
* filer: test CockroachDB collation detection
Cover the CockroachDB skip path and the locale-aware Postgres force path
with go-sqlmock.
Chris Lu