new-repl creates non-satisfied .ghc.environment specification (cabal 2.1)

reproduce:

1) create empty lib-only package "testpackage"
2) `cabal new-configure -w $MYGHCPATH`
3) `cabal new-repl`

env file looks like this; note that the "inplace" entry is not satisfied until we `new-build`:

~~~~
> cat .ghc.environment.x86_64-linux-8.0.2
-- This is a GHC environment file written by cabal. This means you can
-- run ghc or ghci and get the environment of the project as a whole.
-- But you still need to use cabal repl $target to get the environment
-- of specific components (libs, exes, tests etc) because each one can
-- have its own source dirs, cpp flags etc.
--
clear-package-db
global-package-db
package-db $HOME/.cabal/store/ghc-8.0.2/package.db
package-db dist-newstyle/packagedb/ghc-8.0.2
package-id testpackage-0.1.0.0-inplace
package-id base-4.9.1.0
package-id ghc-prim-0.5.0.0
package-id rts
package-id integer-gmp-1.0.0.1