Make sure HAVE_LIBSSL is defined, even when using pkg-config

Without this, the configure script assumes and states that OpenSSL will
be used, but the code won't include support for it because there we use
the "HAVE_LIBSSL" define to test for it ("#ifdef HAVE_LIBSSL").

So define the latter when pkg-config(1) is used, too.

This fixes #257, a regression introduced by commit ad86a41ee :-/

configure.ng

@@ -465,7 +465,8 @@ AC_ARG_WITH(openssl,
 				LDFLAGS="-L$withval/lib $LDFLAGS"
 			fi
 			PKG_CHECK_MODULES([OPENSSL], [libssl libcrypto],
-				[LIBS="$LIBS $OPENSSL_LIBS" CFLAGS="$CFLAGS $OPENSSL_CFLAGS"],
+				[LIBS="$LIBS $OPENSSL_LIBS" CFLAGS="$CFLAGS $OPENSSL_CFLAGS"
+				AC_DEFINE(HAVE_LIBSSL, 1)],
 				[AC_CHECK_LIB(crypto, BIO_s_mem)
 				AC_CHECK_LIB(ssl, SSL_new)]
 			)