Incorrect thread synchronisation in HttpWebConnection

[rschwietzke]

HttpWebConnection is incorrectly using an unsynchronize WeakHashMap for a task that should be done by ThreadLocal. This breaks the state of the map and might lead to infinite loops. We encounter that right now.

PR in flight.

[rbri]

Ups ...

[rschwietzke]

See #1015

[rbri]

Thanks for the PR

[rschwietzke]

We incorporated a patch into XLT and could verify that the faulty behavior is gone.