Operations to initialize and manipulate the repository cache database.
Author: Michael Hanus
Version: March 2018
| repositoryCacheDB
                  ::  Config -> StringThe database containing the repository cache. | 
| tryWriteRepositoryDB
                  ::  Config -> IO ([LogEntry],Either LogEntry ())Writes the repository database with the current repository index if the command sqlite3is in the path. | 
| addPackagesToRepositoryDB
                  ::  Config -> Bool -> [Package] -> IO ([LogEntry],Either LogEntry ()) | 
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                       The database containing the repository cache. | 
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                      Writes the repository database with the current repository index
if the command  | 
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