threading: Add factory that creates curl session for each thread.

When creating a repo with an import url pointing to another repo on the same enterprise instance
we call the vcssserver to check the url. The vcsserver then calls to enterprise to verify the url.
This leads to two threads using the same cur session.

rhodecode/lib/vcs/client_http.py

@@ -31,6 +31,7 @@ implementation.
 
 import copy
 import logging
+import threading
 import urllib2
 import urlparse
 import uuid
@@ -38,7 +39,7 @@ import uuid
 import msgpack
 import requests
 
-from . import exceptions
+from . import exceptions, CurlSession
 
 
 log = logging.getLogger(__name__)
@@ -216,3 +217,17 @@ class VcsHttpProxy(object):
         headers = iterator.next()
 
         return iterator, status, headers
+
+
+class ThreadlocalSessionFactory(object):
+    """
+    Creates one CurlSession per thread on demand.
+    """
+
+    def __init__(self):
+        self._thread_local = threading.local()
+
+    def __call__(self):
+        if not hasattr(self._thread_local, 'curl_session'):
+            self._thread_local.curl_session = CurlSession()
+        return self._thread_local.curl_session