Add internal support for hc-pkg recache and --enable-multi-instance
Add internal support for hc-pkg recache and --enable-multi-instance

Invocation support but not used yet.

randen/cabal,garetxe/cabal,edsko/cabal,kolmodin/cabal,lukexi/cabal,Heather/cabal,bennofs/cabal,bennofs/cabal,sopvop/cabal,gbaz/cabal,themoritz/cabal,sopvop/cabal,Heather/cabal,kolmodin/cabal,randen/cabal,sopvop/cabal,thomie/cabal,lukexi/cabal,gbaz/cabal,mydaum/cabal,headprogrammingczar/cabal,edsko/cabal,headprogrammingczar/cabal,thomie/cabal,martinvlk/cabal,themoritz/cabal,garetxe/cabal,mydaum/cabal,martinvlk/cabal,themoritz/cabal