This work around any deviciency/limitation of the clone process. In our case
this ensure the persistent nodemap exist with valid content.
Ideally, the cloning process would also do "the right thing". However since
older server will never be able to do "the right thing". The local workaround
will be necessary anyway.
I am not worried by the performance impact of this as hg clone is non-instant
on large repositories where is could matters. Warming the cache if they are
already correct is very fast. And if they are not already warm, this seems like
a good time to do so.
This impact various test as more cache are now warmed sooner, all the change
should be harmless.