CMake: improve library search, implement install.

Improved library search by check_function_exists_concat() macro:
it does not revert the list of libraries any more.

Improved OpenSSL library search: first find zlib, then search for
openssl libraries that may depend on zlib.

For Unix: openssl libraries can now be detected in nonstandard
locations. Supply CMAKE_LIBRARY_PATH to CMake on command line.

Added installation capability (very basic one yet).