Dump the block information in CSV format

Dump the block information in CSV format

This makes it easy to copy this information into a new file and
process it with tools that understand CSV, e.g. to create histograms
of block utilization.

* reclaim.c (GC_print_block_descr): add n_objs local variable;
separate printed values with a comma; print also size of block in
object units; refactor code for computing total_bytes field.
* reclaim.c (GC_print_block_list): Separate columns in printed table
header with a comma; append "#objs" column to the table.