returns xml fragment.
<response success="true" error="">
if success attribute is "true", the folder list has been retrived successfully like the xml sample below.
if success attribute is "false", the error attribute indicates the encountered error.
<response success="true" error="" folderid="10124" parentid="0" name="Accounting" path="\Accounting" folderfilter="" itemcount="4">
<f id="10137" n="General Ledger" />
<f id="10286" n="Incoming Invoices" />
<f id="10138" n="Payables" />
<f id="10139" n="Receivables" />
</response>