rustpkg: Preliminary work on install command

Mostly just tests (that are ignored); install command is still
stubbed out.

src/librustpkg/context.rs

@@ -0,0 +1,21 @@
+// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Context data structure used by rustpkg
+
+use core::hashmap::HashMap;
+
+pub struct Ctx {
+    // I'm not sure what this is for
+    json: bool,
+    // Cache of hashes of things already installed
+    // though I'm not sure why the value is a bool
+    dep_cache: @mut HashMap<~str, bool>,
+}