cell name from the cell name hash table. So when "cellname rename"
was changed recently to prevent changing the name of a cell that
already exists, the suggested recipe for R-C extraction no longer
works: "load x; flatten y; load y; cellname delete x; cellname
rename y x". Solved by adding a HashRemove() function to the
cell deletion routine. Thanks to Egor Lukyachenko for reporting
the issue (Github issue tracker #467).