-- add driver.Value type and documentation,
convert from interface{} to Value where
appropriate.
-- don't say "subset" anywhere,
-- SubsetValuer -> Valuer
-- SubsetValue -> Value
-- IsParameterSubsetType -> IsValue
-- IsScanSubsetType -> IsScanValue
Fixes#2842
R=golang-dev, r, rsc
CC=golang-dev
https://golang.org/cl/5674084
If the database driver supports the Execer interface but returns
ErrSkip, calling Exec on a transaction was returning the error instead
of using the slow path.
R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/5654044
