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.
Using throw() specifications in function signatures is not only
not required in C++, it is considered deprecated for
[various reasons](https://stackoverflow.com/questions/1055387/throw-keyword-in-functions-signature).
It is not implemented by any of the common C++ compilers. The usage is
also inconsistent with the rest of the source code.
There was a previous assumption that blockindex would be quite small. With addressindex
and spentindex enabled the blockindex is much larger and the amount of cache allocated for
it should also increase. Furthermore, enabling compression should decrease the amount of
disk space required and less data to write/read. The default leveldb max_open_files is set to
1000, for the blockindex the default is set to 1000 with compression. The 64 value that is
current is kept for the utxo database and does not enable compression. Two additional options
are added here to be able to configure the values for leveldb and the block index:
- `-dbmaxopenfiles` A number of files for leveldb to keep open
- `-dbcompression` Boolean 0 or 1 to enable snappy leveldb compression
