winhttp/tests: Fix an intermittent test failure on Windows XP/Vista.

dlls/winhttp/tests/winhttp.c

@@ -319,7 +319,7 @@ static void test_SendRequest (void)
     static CHAR post_data[] = "mode=Test";
     static const char test_post[] = "mode => Test\0\n";
     HINTERNET session, request, connection;
-    DWORD header_len, optional_len, total_len, bytes_rw, size, err;
+    DWORD header_len, optional_len, total_len, bytes_rw, size, err, disable;
     DWORD_PTR context;
     BOOL ret;
     CHAR buffer[256];
@@ -350,6 +350,12 @@ static void test_SendRequest (void)
     ret = WinHttpSetOption(request, WINHTTP_OPTION_CONTEXT_VALUE, &context, sizeof(context));
     ok(ret, "WinHttpSetOption failed: %u\n", GetLastError());
 
+    /* writing more data than promised by the content-length header causes an error when the connection
+       is resued, so disable keep-alive */
+    disable = WINHTTP_DISABLE_KEEP_ALIVE;
+    ret = WinHttpSetOption(request, WINHTTP_OPTION_DISABLE_FEATURE, &disable, sizeof(disable));
+    ok(ret, "WinHttpSetOption failed: %u\n", GetLastError());
+
     context++;
     ret = WinHttpSendRequest(request, content_type, header_len, post_data, optional_len, total_len, context);
     err = GetLastError();