MB-16645: Maximum view header size is wrong
MB-16645: Maximum view header size is wrong

The header size of a view index file can be way bigger than 64KB.
Based on the code in `couch_set_view_util:group_to_header_bin/1`
function, the maximum size is below 20MB.

The currently exact maximum size is `20144805` (uncompressed) which comes
from the following calculation.

    16 + 1 + 2 + 128 + 128 + 128 + (2 + 8*1024) + 2+65535 +
    (2 + 256*(2+65535)) + 1 + (2 + 1024*2) + (3*2 + 1024*2) + (2 + 1024*8) +
    (2 + (2 + 2 + 25*128)*1024)

It makes sense when you look at `couch_set_view_util:group_to_header_bin/1`
where the Erlang terms get encoded into the final binary format.

Change-Id: Icb2114b53ae7da5bf5fd45cd34fdea4a5a9d3cbd
Reviewed-on: http://review.couchbase.org/56386
Reviewed-by: Dave Rigby <a09264da4832c7ff1d3bf1608a19f4b870f93750@couchbase.com>
Reviewed-by: Abhishek Singh <0731fdeb307910eeaae4e58897b7baaba45e054b@couchbase.com>
Tested-by: buildbot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>

couchbaselabs/couchstore,couchbaselabs/couchstore,couchbaselabs/couchstore