Fix symlinking of new projects

We weren't copying these lists, so the += was actually changing the
underlying lists.

When a new project was added to the manifest, we run _CheckDirReference
against the manifest project with share_refs=True, which added the
working_tree_* to the shareable_* lists. Then, when we load the new
manifest and create the new project, it uses the lists that already
contain the working_tree_* files, even though we passed
share_refs=False.

This happens reliably under the above conditions, but doesn't seem to
happen when syncing a fresh tree. So we've got a mixture of links that
may need to be cleaned up later. This patch will just stop it from
happening in the future.

Change-Id: Ib7935bfad78af1e494a75e55134ec829f13c2a41

project.py

@@ -2315,8 +2315,8 @@ class Project(object):
         self.bare_git.symbolic_ref('-m', msg, ref, dst)
 
   def _CheckDirReference(self, srcdir, destdir, share_refs):
-    symlink_files = self.shareable_files
-    symlink_dirs = self.shareable_dirs
+    symlink_files = self.shareable_files[:]
+    symlink_dirs = self.shareable_dirs[:]
     if share_refs:
       symlink_files += self.working_tree_files
       symlink_dirs += self.working_tree_dirs
@@ -2344,8 +2344,8 @@ class Project(object):
       copy_all: If true, copy all remaining files from |gitdir| -> |dotgit|.
           This saves you the effort of initializing |dotgit| yourself.
     """
-    symlink_files = self.shareable_files
-    symlink_dirs = self.shareable_dirs
+    symlink_files = self.shareable_files[:]
+    symlink_dirs = self.shareable_dirs[:]
     if share_refs:
       symlink_files += self.working_tree_files
       symlink_dirs += self.working_tree_dirs