Only copy sharename up from rap_to_pjobid

Only copy sharename up from rap_to_pjobid

Why?? :-)

Another one of the little micro-optimizations that I just came across: If you
allocate a variable in a sub-block like the "fstring sharename" in
write_file(), gcc even with -O3 will allocate this variable unconditionally on
the stack at the beginning of the routine. So with eliminating this fstring we
cut 256 bytes of stack in a very hot code path writing to a file. It might make
us a bit more cache-friendly.

This would probably not be worth a second look if it involved larger code
changes, but this one was just too simple to let it pass :-)