Add new compiler independent package db utils
Add new compiler independent package db utils

Add doesPackageDBExist and deletePackageDB, and export the new
createPackageDB. This gives a more complete compiler-independent API for
package db manipulation.

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