CMake and OpenSSL support!

Hi, here are some news from the front!

We migrated the build system to CMake. SCons is still usable, but should be used only for development purposes. Please note that autotools scripts should now be generated with CMake, as it has been removed from SCons script.

Thanks to the help of Mehmet Bozkurt, VMime now supports OpenSSL for SSL/TLS features, in addition to the existing support for GnuTLS.

We hope these new features will make deployment of VMime easier.

Build against libgnutls >= 2.8

VMime 0.9.0 autoconf build process uses the libgnutls-config script to search for GNU TLS (by using AM_PATH_LIBGNUTLS). This script is deprecated and not shipped in gnutls 2.8.0 and later; pkg-config should now be used. Andreas Metzler provided a patch for fixing this.