added even more nginx debugging logs to the ngx.semaphore API implementation.

Author: agentzh

src/ngx_http_lua_semaphore.c

@@ -376,6 +376,9 @@ ngx_http_lua_ffi_semaphore_wait(ngx_http_request_t *r,
     wait_co_ctx->data = sem;
     wait_co_ctx->cleanup = ngx_http_lua_semaphore_cleanup;
 
+    ngx_log_debug0(NGX_LOG_DEBUG_HTTP, sem->log, 0,
+                   "http lua semaphore wait yielding");
+
     return NGX_AGAIN;
 }