Add filtering for curl debug output.

Add CURLTR debug channel for libcurl API calls,
and use CURLIO only for libcurl debug output.
Note: need to set gDebugCurlTerse to true for
filtering to take effect, then pass 'debug_on'
to the LLHttpClient methods that require debugging.

indra/llmessage/debug_libcurl.h

@@ -86,4 +86,9 @@ extern char* debug_curl_version(void);
 
 #endif // !COMPILING_DEBUG_LIBCURL_CC
 
+extern bool gDebugCurlTerse;					// With this set,
+void debug_curl_add_easy(CURL* handle);			// only output debug output for easy handles added with this function.
+void debug_curl_remove_easy(CURL* handle);
+bool debug_curl_print_debug(CURL* handle);
+
 #endif // DEBUG_LIBCURL