Before this PR, config parsing would accept duplicate job names. `zrepl
daemon` would later fail to start with a panic. But tools like `zrepl
configcheck` would pass.
This PR adds a check to ensure job names are unique.
Similarly, internal job names were not being rejected by config parsing
Move that check to parse-time as well.
Last, drive-by change: remove `internal/config/config_include_test.go`
introduced in #856 . These aren't necessary because there is already a
wildcard test for all valid configs.
This PR adds the complimentary "invalid config" wildcard test.
Christian Schwarz