add: experimental (slightly buggy) SLIME-TRACE-DIALOG-REFETCH-TRACES

* with supporting SWANK-TRACE-DIALOG:REPORT-PARTIAL-TREE
* with pretty progress bar (but is this useful?)
* buggy at least when multiple requests in succession are performed
fix: reset *ID* to 0 on SWANK-TRACE-DIALOG:CLEAR-TRACE-TREE
fix: correctly report atomic retval lists such as :EXITED-NON-LOCALLY
minor: whitespace