A common complaint with the new package environment files feature is
that it's not obvious when package environments have been picked up.
This patch applies the same strategy that was already used for .ghci files
(which exhibit similar potential for confusion, c.f. Trac #11389) to package
environment files.

For instance, this new notification looks like below for GHCi invocation which
loads both, a GHCi configuration as well as a package environment.

GHCi, version 8.5.20180512: http://www.haskell.org/ghc/  :? for help
Loaded package environment from /tmp/parsec-3.1.13.0/.ghc.environment.x86_64-linux-8.5.20180512
Loaded GHCi configuration from /home/hvr/.ghci
Prelude>

Addresses Trac #15145