Adjust trace_sort log messages.
The project message style guide dictates: "When citing the name of an
object, state what kind of object it is". The parallel CREATE INDEX
patch added a worker number to most of the trace_sort messages within
tuplesort.c without specifying the object type. Bring these messages
into compliance with the style guide.
We're still treating a leader or serial Tuplesortstate as having worker
number -1. trace_sort is a developer option, and these two cases are
highly comparable, so this seems appropriate.
Per complaint from Tom Lane.
Discussion: https://postgr.es/m/8330.
1540831863@sss.pgh.pa.us
Backpatch: 11-, where parallel CREATE INDEX was introduced.