Pull gclient revision 72 and add the gclient unit test.

README.gclient

+# Copyright 2008-2009, Google Inc.
+
+gclient is a tool for managing a modular checkout of source code
+from multiple source code repositories.  It wraps underlying source
+code management commands to provide support for distributing tree
+updates, status commands, and diffs across multiple checked-out
+working directories.
+
+
+The gclient script is controlled by a ".gclient" file at the top
+of a directory tree which will contain source code from multiple
+locations.  A ".gclient" file is a Python script that defines a list
+of "solutions" with the following format:
+
+    solutions = [
+      { "name"        : "src",
+        "url"         : "svn://svnserver/component/trunk/src",
+        "custom_deps" : {
+          # To use the trunk of a component instead of what's in DEPS:
+          #"component": "https://svnserver/component/trunk/",
+          # To exclude a component from your working copy:
+          #"data/really_large_component": None,
+        }
+      },
+    ]
+
+A "solution" is a collection of component pieces of software that will
+be checked out in a specific directory layout for building together.
+
+Each entry in the "solutions" list is defined by a Python dictionary
+that contains the following items:
+
+    name
+        The name of the directory in which the solution will be
+        checked out.
+
+    url
+        The URL from which this solution will be checked out.
+        gclient expects that the checked-out solution will contain a
+        file named "DEPS" that in turn defines the specific pieces
+        that must be checked out to create the working directory
+        layout for building and developing the solution's software.
+
+    custom_deps
+        A dictionary containing optional custom overrides for entries
+        in the solution's "DEPS" file.  This can be used to have
+        the local working directory *not* check out and update specific
+        components, or to sync the local working-directory copy of a
+        given component to a different specific revision, or a branch,
+        or the head of a tree. It can also be used to append new entries
+        that do not exist in the "DEPS" file.
+
+Within each checked-out solution, gclient expects to find a file
+named "DEPS" which defines the different component pieces of
+software that must be checked out for the solution.  The "DEPS"
+file is a Python script that defines a dictionary named "deps":
+
+    deps = {
+      "src/outside" : "http://outside-server/trunk@1234",
+      "src/component" : "svn://svnserver/component/trunk/src@77829",
+      "src/relative" : "/trunk/src@77829",
+    }
+
+Each item in the "deps" dictionary consists of a key-value pair.
+The key is the directory into which the component will be checked
+out, relative to the directory containing the ".gclient" file.
+The value is the URL from which that directory will be checked out.
+If there is no address scheme (that is, no "http:" or "svn:" prefix),
+then the value must begin with a slash and is treated relative to the
+root of the solution's repository.
+
+The URL typically contains a specific revision or change number (as
+appropriate for the underlying SCM system) to "freeze" the external
+software at a specific, known state.  Alternatively, if there is no
+revision or change number, the URL will track the latest changes on the
+specific trunk or branch.