Include the output name in the GC root link

Output names are now appended to resulting GC symlinks, e.g. by
nix-build.  For backwards compatibility, if the output is named "out",
nothing is appended.  E.g. doing "nix-build -A foo" on a derivation
that produces outputs "out", "bin" and "dev" will produce symlinks
"./result", "./result-bin" and "./result-dev", respectively.

src/libmain/shared.hh

@@ -26,7 +26,6 @@ MakeError(UsageError, nix::Error);
 class StoreAPI;
 
 /* Ugh.  No better place to put this. */
-Path makeRootName(const Path & gcRoot, int & counter);
 void printGCWarning();
 
 void printMissing(StoreAPI & store, const PathSet & paths);