ecap_clamav_adapter uses tr1::static_pointer_cast

[Patrick Welche]

https://bugs.launchpad.net/ecap/+bug/1595488

explains why a move to C++11 in squid's footsteps seems necessary.

Code like:

      const libecap::shared_ptr<Service> s =
                    std::tr1::static_pointer_cast<Service>(self);

in ecap_clamav_adapter's src/Service.cc shows that the libecap::shared_ptr dance in libecap's memory.h, while a good idea, would end up breaking in practice.

[Patrick Welche (prlw1)]

Update to C++11

As per https://bugs.launchpad.net/ecap/+bug/1595488 it seems that
moving to requiring C++11 in line with squid is necessary.

- Enforce C++11 requirement using autoconf-archive macros.
- Remove trace of std::tr1.
- Replace deprecated auto_ptr with unique_ptr.
- As you already depend on pkg-config to find libecap, do
  the same for libclamav. (If you prefer, I could go the other
  way and replace pkg-config with real autoconf detection for
  libecap.)
- add ax_pthread.m4 to fix missing macros.

[Patrick Welche (prlw1)]

Stop using libecap/common/memory.h and std::shared_ptr and friends directly.