Dbwrapper used GetSerializeSize() to compute the size of the buffer
to preallocate. For some cases (specifically: CCoins) this requires
a costly compression call. Avoid this by just using fixed size
preallocations instead.
Given that in default GetSerializeSize implementations created by
ADD_SERIALIZE_METHODS we're already using CSizeComputer(), get rid
of the specialized GetSerializeSize methods everywhere, and just use
CSizeComputer. This removes a lot of code which isn't actually used
anywhere.
For CCompactSize and CVarInt this actually removes a more efficient
size computing algorithm, which is brought back in a later commit.
Zcash: Makes future extensions easier.
Original description (when this was introduced upstream):
Pass parent wrapper directly instead of obfuscation key. This
makes it possible for other databases which re-use this code
to use other properties from the database.
Add a namespace dbwrapper_private for private functions to be used
only in dbwrapper.h/cpp and dbwrapper_tests.
