Non-ascii sctring saving fix

Before saving string on disc (which probably work very well), we
send it in node with "Content-Length" header. Probably ".length" operator
gives wrong number if string contains non-ascii chars (smaller, than it must be).
test: cleanup after the previous commit

Move the test for non-ASCII requests to test/DebuggerClient,
make it independent on the script id values assigned by V8.