c-ares support for curl. (py)curl updates.

Hi Diego,

as discussed via email, the DBS 3 Migration Service has some problems with pycurl and multi-threading. pycurl itself is thread-safe, however the DNS lookup is not. The suggestion on http://linux.die.net/man/3/libcurl-tutorial is to disable signals, which I did for DBS 3. The disadvantage is, that DNS timeouts are not caught anymore in that case. The solution is to use c-ares for the DNS lookup. I have added a c-ares.spec and configured curl to build against c-ares.

In addition, I have upgraded curl and pycurl to the latest release to enable shared SSL session id caches between different threads, to reduce the load on cmsweb through authentication during migration requests. 

I have tested DBS 3 Server, DBS 3 Migration Service and DBS 3 Client, everything seems to be fine.

Could you review and merge, please?

Thanks,
Manuel