win: Fix failing tests. (neovim#201)

- test_vim.test_command: close the file before unlink().

- test_vim.test_chdir was failing for two reasons. First because
  of missing Windows-specific handling of path names in
  find_file_in_path_option in file_search.c in Neovim core
  (neovim/neovim#4711). Second because although `:cd /` 
  works, getcwd() prepends the drive-letter.

Closes neovim#166

test/test_vim.py

@@ -21,7 +21,8 @@ def test_command():
     vim.command('normal itesting\npython\napi')
     vim.command('w')
     ok(os.path.isfile(fname))
-    eq(open(fname).read(), 'testing\npython\napi\n')
+    with open(fname) as f:
+      eq(f.read(), 'testing\npython\napi\n')
     os.unlink(fname)
 
 
@@ -63,8 +64,10 @@ def test_strwidth():
 @with_setup(setup=cleanup)
 def test_chdir():
     pwd = vim.eval('getcwd()')
+    root = os.path.abspath(os.sep)
+    # We can chdir to '/' on Windows, but then the pwd will be the root drive
     vim.chdir('/')
-    eq(vim.eval('getcwd()'), '/')
+    eq(vim.eval('getcwd()'), root)
     vim.chdir(pwd)
     eq(vim.eval('getcwd()'), pwd)