Misc build improvements

    - Clean up bundled build location
    - Check that we've been provided a valid build type
    - FORCEfully set the CMAKE_BUILD_TYPE variable, if it has not, already.
    - Switched from curl's cmake scripts to autoconf. Curl doesn't seem to
      officially support its cmake build scripts. Curl 7.30.0 doesn't build
      using cmake -DENABLE_IPV6=On ...
    - Explicitly building curl with SSL support
    - Add FindPCRE.cmake, so we can do a better job of tracking down PCRE libs.
    - Ensure that HAVE_PCRE is defined via config.h
    - Fix typo for OpenSSL include directories