Fixes for PCRE, OpenSSL

- 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
Improve bundled curl building

- 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
Properly handle CMAKE_BUILD_TYPE

- Check that we've been provided a valid build type
- FORCEfully set the CMAKE_BUILD_TYPE variable, if it has not, already.
Clean up bundled build location
Properly reference PCRE_INCLUDE_DIR
Merge pull request #198 from justfalter/misc_build_improvements

Misc build improvements