ghc-pkg unregister --user/--global/--package-conf not normative

[guest]

For package P,

"ghc-pkg unregister --user P" drops the global package if P is not in user.

"ghc-pkg unregister --global P" drops the user package if P is in user.

"ghc-pkg unregister --package-conf=<dir> P" drops the user or the global package, preferring the user one, if P is not found in <dir>.

Same with "ghc-pkg --user unregister P", "ghc-pkg unregister P --user", etc.

GHC versions 6.10, 6.12, 7.0, 7.2.