Re: [PATCH 4/5] index: make index.threads=true enable ieot and eoie

> If a user explicitly sets
> 
> 	[index]
> 		threads = true
> 
> to read the index using multiple threads, ensure that index writes
> include the offset table by default to make that possible.  This
> ensures that the user's intent of turning on threading is respected.
> 
> In other words, permit the following configurations:
> 
> - index.threads and index.recordOffsetTable unspecified: do not write
>    the offset table yet (to avoid alarming the user with "ignoring IEOT
>    extension" messages when an older version of Git accesses the
>    repository) but do make use of multiple threads to read the index if
>    the supporting offset table is present.
> 
>    This can also be requested explicitly by setting index.threads=true,
>    0, or >1 and index.recordOffsetTable=false.
> 
> - index.threads=false or 1: do not write the offset table, and do not
>    make use of the offset table.
> 
>    One can set index.recordOffsetTable=false as well, to be more
>    explicit.
> 
> - index.threads=true, 0, or >1 and index.recordOffsetTable unspecified:
>    write the offset table and make use of threads at read time.
> 
>    This can also be requested by setting index.threads=true, 0, >1, or
>    unspecified and index.recordOffsetTable=true.
> 
> Fortunately the complication is temporary: once most Git installations
> have upgraded to a version with support for the IEOT and EOIE
> extensions, we can flip the defaults for index.recordEndOfIndexEntries
> and index.recordOffsetTable to true and eliminate the settings.
>