adding options: --package-conf and --no-user-package-conf

These command line options work just like the similar-named GHC flags.
They are useful when working with non-standard package databases.

GHCMod.hs

@@ -40,6 +40,8 @@ defaultOptions = Options {
     convert = toPlain
   , hlintOpts = []
   , operators = False
+  , packageConfs = []
+  , useUserPackageConf = True
   }
 
 argspec :: [OptDescr (Options -> Options)]
@@ -52,6 +54,12 @@ argspec = [ Option "l" ["tolisp"]
           , Option "o" ["operators"]
             (NoArg (\opts -> opts { operators = True }))
             "print operators, too"
+          , Option ""  ["package-conf"]
+            (ReqArg (\p opts -> opts { packageConfs = p : packageConfs opts }) "path")
+            "additional package database"
+          , Option ""  ["no-user-package-conf"]
+            (NoArg (\opts -> opts{ useUserPackageConf = False }))
+            "do not read the user package database"
           ]
 
 parseArgs :: [OptDescr (Options -> Options)] -> [String] -> (Options, [String])