Work around for 'version `OPENSSL_1.0.0' not found'

When linking against the prebuilt libcrypto.so.1.0.0 and
libssl.so.1.0.0 there is a problem running the viewer in
gdb (on debian) because gdb links with libpython2.7.so
which needs a newer openssl on my system (OPENSSL_1.0.1).

The patch allows to work around this problem by defining
-DUSE_SYSTEM_OPENSSL:BOOL=ON when configuring, which then
causes the viewer to be compiled against the system libs.
(If you already installed the prebuilt, you have to manually
remove them with script/install.py --uninstall openSSL).

The prebuilt libcurl expects a function SSLv2_client_method
however, which is not present in my openssl system libs.
A stub was added which is possible because the function
in question isn't used anyway.

indra/cmake/OpenSSL.cmake

@@ -4,9 +4,9 @@ include(Prebuilt)
 set(OpenSSL_FIND_QUIETLY ON)
 set(OpenSSL_FIND_REQUIRED ON)
 
-if (STANDALONE)
+if (STANDALONE OR USE_SYSTEM_OPENSSL)
   include(FindOpenSSL)
-else (STANDALONE)
+else (STANDALONE OR USE_SYSTEM_OPENSSL)
   use_prebuilt_binary(openSSL)
   if (WINDOWS)
     set(OPENSSL_LIBRARIES ssleay32 libeay32)
@@ -14,7 +14,7 @@ else (STANDALONE)
     set(OPENSSL_LIBRARIES ssl)
   endif (WINDOWS)
   set(OPENSSL_INCLUDE_DIRS ${LIBS_PREBUILT_DIR}/${LL_ARCH_DIR}/include)
-endif (STANDALONE)
+endif (STANDALONE OR USE_SYSTEM_OPENSSL)
 
 if (LINUX OR DARWIN)
   set(CRYPTO_LIBRARIES crypto)

indra/llmessage/aicurl.cpp

@@ -1014,6 +1014,8 @@ CURLcode CurlEasyRequest::curlCtxCallback(CURL* curl, void* sslctx, void* parm)
 	options |= SSL_OP_NO_TLSv1_1;
   }
 #else
+  // This is expected when you compile against the headers of a version < 1.0.1 and then link at runtime with version >= 1.0.1.
+  // Don't do that.
   llassert_always(!need_renegotiation_hack);
 #endif
   SSL_CTX_set_options(ctx, options);
@@ -1417,3 +1419,16 @@ CurlMultiHandle::~CurlMultiHandle()
 }
 
 } // namespace AICurlPrivate
+
+extern "C" {
+
+// Keep linker happy.
+SSL_METHOD *SSLv2_client_method(void)
+{
+  // Never used.
+  llassert_always(false);
+  return NULL;
+}
+
+}
+