Don't cache dulwich Repos, in pararell multithreaded evniroment dulwich pack file openers

can break badly. We need to create Repo() objects always for each call, even when it's
taken from cache.
Fixed issue with dulwich filedescriptor leak ref  #573

rhodecode/lib/vcs/backends/git/repository.py

@@ -54,7 +54,18 b' class GitRepository(BaseRepository):'
                  update_after_clone=False, bare=False):
 
         self.path = abspath(repo_path)
-        self._repo = self._get_repo(create, src_url, update_after_clone, bare)
+        repo = self._get_repo(create, src_url, update_after_clone, bare)
+        self.bare = repo.bare
+
+        self._config_files = [
+            bare and abspath(self.path, 'config') or abspath(self.path, '.git',
+                'config'),
+            abspath(get_user_home(), '.gitconfig'),
+        ]
+
+    @property
+    def _repo(self):
+        repo = Repo(self.path)
         #temporary set that to now at later we will move it to constructor
         baseui = None
         if baseui is None:
@@ -62,19 +73,15 b' class GitRepository(BaseRepository):'
             baseui = ui()
         # patch the instance of GitRepo with an "FAKE" ui object to add
         # compatibility layer with Mercurial
-        setattr(self._repo, 'ui', baseui)
-
-        try:
-            self.head = self._repo.head()
-        except KeyError:
-            self.head = None
+        setattr(repo, 'ui', baseui)
+        return repo
 
-        self._config_files = [
-            bare and abspath(self.path, 'config') or abspath(self.path, '.git',
-                'config'),
-            abspath(get_user_home(), '.gitconfig'),
-        ]
-        self.bare = self._repo.bare
+    @property
+    def head(self):
+        try:
+            return self._repo.head()
+        except KeyError:
+            return None
 
     @LazyProperty
     def revisions(self):