Fix a regression due to:
Remove an arena_bin_run_size_calc() constraint.
2a6f2af6e446a98a635caadd281a23ca09a491cb
The removed constraint required that small run headers fit in one page,
which indirectly limited runs such that they would not cause overflow in
arena_run_regind(). Add an explicit constraint to
arena_bin_run_size_calc() based on the largest number of regions that
arena_run_regind() can handle (2^11 as currently configured).
47e57f9bda