Expose a perl method to query a derivation

Just doing a very stupid thing taking as argument a serialised drv
output and returning a serialised realisation.

This is needed for `nix-serve` to handle ca derivations

perl/lib/Nix/Store.pm

@@ -22,6 +22,7 @@ our @EXPORT = qw(
     derivationFromPath
     addTempRoot
     getBinDir getStoreDir
+    queryRawRealisation
 );
 
 our $VERSION = '0.15';