Fixes Bug 926507 - enhancements to jDump processing

Now that we've got the correct stackwalker, I was surprised by its output and had to make adjustments:

1) status is a string rather than an error code
2) pDump/jDump sentinel should be discarded and not left with the pDump output
3) pDump reading needs to spool additional threads from the buffer in order to detect the sentinel