[fix] Make buildout.rmtree working with symlink as a path argument

https://bugs.launchpad.net/zc.buildout/+bug/144228

src/zc/buildout/rmtree.py

@@ -16,7 +16,6 @@
 import shutil
 import os
 import doctest
-import time
 
 def rmtree (path):
     """
@@ -26,6 +25,8 @@ def rmtree (path):
     process (e.g. antivirus scanner). This tries to chmod the
     file to writeable and retries 10 times before giving up.
 
+    Also it tries to remove symlink itself if a symlink as passed as
+    path argument.
     >>> from tempfile import mkdtemp
 
     Let's make a directory ...
@@ -41,6 +42,8 @@ def rmtree (path):
 
     >>> foo = os.path.join (d, 'foo')
     >>> with open (foo, 'w') as f: _ = f.write ('huhu')
+    >>> bar = os.path.join (d, 'bar')
+    >>> os.symlink(bar, bar)
 
     and make it unwriteable
 
@@ -52,21 +55,51 @@ def rmtree (path):
 
     and now the directory is gone
 
+    >>> os.path.isdir (d)
+    0
+
+    Let's make a directory ...
+
+    >>> d = mkdtemp()
+
+    and make sure it is actually there
+
+    >>> os.path.isdir (d)
+    1
+
+    Now create a broken symlink ...
+
+    >>> foo = os.path.join (d, 'foo')
+    >>> os.symlink(foo + '.not_exist', foo)
+
+    rmtree should be able to remove it:
+
+    >>> rmtree (foo)
+
+    and now the directory is gone
+
+    >>> os.path.isdir (foo)
+    0
+
+    cleanup directory
+
+    >>> rmtree (d)
+
+    and now the directory is gone
+
     >>> os.path.isdir (d)
     0
     """
     def retry_writeable (func, path, exc):
-        os.chmod (path, 384) # 0600
-        for i in range(10):
-            try:
-                func (path)
-                break
-            except OSError:
-                time.sleep(0.1)
-        else:
-            # tried 10 times without success, thus
-            # finally rethrow the last exception
+        if func is os.path.islink:
+            os.unlink(path)
+        elif func is os.lstat or func is os.open:
+            if not os.path.islink(path):
                 raise
+            os.unlink(path)
+        else:
+            os.chmod(path, 0o600)
+            func(path)
 
     shutil.rmtree (path, onerror = retry_writeable)