Use binary search to speedup checkUnload
We are iterating through all object code for each heap objects when
checking whether object code can be unloaded. For large projects in
GHCi, this can be very expensive due to the large number of object code
that needs to be loaded/unloaded. To speed it up, this arrangess all
mapped sections of unloaded object code in a sorted array and use binary
search to check if an address location fall on them.