Format specification: Need to clarify the description in section III.I. Disk Format: Level 1I - Shared Object Header Message Table

[vchoi-hdfgroup]

Describe the bug
The variable N is used as the cap for the shared object header message indexes in the Shared Object Header Message Table. At the same time, N is also used for the records in the Shared Message Record LIst.

Expected behavior
--Use a different variable e.g. K for the records in the shared message record list.
--The number of records in the shared message record list is determined by the Number of Messages field for each index entry in the shared object header message table.