This largely avoids a large buffer copy which would accumulate inside proxyReader{}
This patch also implements "initialize()" function to init and populate data
on all the existing buckets, avoiding the redundant ListBuckets() invoked by
every API call.
Using same object cache as regular objects for multiparts causes deadlocks during object expiration routine.
As a side affect this also fixes the bug of listing multiparts during regular 'listing' of objects.
Harshavardhana