Modify the ranges_access() helper function to be able to lookup the address...

Modify the ranges_access() helper function to be able to lookup the address range in a block given an address. Since blocks can have multiple discontiguous ranges, it helps to be able to get the current address range for the current block in a frame. This can be used in code like:

curr_block_range = lldb.frame.block.range[lldb.frame.addr]

llvm-svn: 159289