Writing a slice to an existing bin

If the slice is being written to an existing bin:

1. The slicename is hashed to determine bin file and bin number.
2. Existence of an in-memory pointer indicates the bin in question already exists on disk.
3. The bin location is retrieved from the in-memory pointers.
4. The entire bin is read into system memory.
5. The bin is modified to include the new slice data.
6. The entire new bin is appended to the end of the bin file.
7. The in-memory bin pointers are updated to reflect the new position of this bin.
8. The Pointer File is updated with the new location of the bin.