Bug#4102 - Failure to build mod_tls when using static libcrypto due to libdl
linker errors.
Fix another place where the libdl linker flag may need to come earlier in
the list.
Bug#4102 - Failure to build mod_tls when using static libcrypto due to libdl
linker errors.

In the course of fixing this issue, I also fixed problems with configure's
detection of EC support in OpenSSL, and make it possible for mod_sftp to
build without zlib support.
Improve the detection of zlib support, and handling of the results, for
mod_sftp.
Make sure to add -lz, when needed, to the building of a DSO mod_sftp.
Make sure that if zlib support is lacking, mod_sftp does not to try negotiate
compression during the key exchange.
Updating NEWS.
Merge pull request #43 from proftpd/build-openssl-libdl-errors-bug4102

Bug#4102 - Failure to build mod_tls when using static libcrypto due to libdl linker errors