Don't specify a point size for "Wallet"
Don't use -dbcache for BDB anymore

-dbcache was originally used to set the maximum buffer size in the
BDB environment, and was later changed to set the chainstate cache
and leveldb caches. No need to use it for BDB now that only the
wallet remains there.

This should reduce memory allocation (but not necessarily memory
usage) a bit.
P2P: parse network datastream into header/data components in socket thread

Replaces CNode::vRecv buffer with a vector of CNetMessage's.  This simplifies
ProcessMessages() and eliminates several redundant data copies.

Overview:

* socket thread now parses incoming message datastream into
  header/data components, as encapsulated by CNetMessage
* socket thread adds each CNetMessage to a vector inside CNode
* message thread (ProcessMessages) iterates through CNode's CNetMessage vector

Message parsing is made more strict:

* Socket is disconnected, if message larger than MAX_SIZE
  or if CMessageHeader deserialization fails (latter is impossible?).
  Previously, code would simply eat garbage data all day long.
* Socket is disconnected, if we fail to find pchMessageStart.
  We do not search through garbage, to find pchMessageStart.  Each
  message must begin precisely after the last message ends.

ProcessMessages() always processes a complete message, and is more efficient:

* buffer is always precisely sized, using CDataStream::resize(),
  rather than progressively sized in 64k chunks.  More efficient
  for large messages like "block".
* whole-buffer memory copy eliminated (vRecv -> vMsg)
* other buffer-shifting memory copies eliminated (vRecv.insert, vRecv.erase)
P2P, cosmetic: break out buffer send(2) code into separate function
P2P: improve RX/TX flow control

1) "optimistic write": Push each message to kernel socket buffer immediately.

2) If there is write data at select time, that implies send() blocked
   during optimistic write.  Drain write queue, before receiving
   any more messages.

This avoids needlessly queueing received data, if the remote peer
is not themselves receiving data.

Result: write buffer (and thus memory usage) is kept small, DoS
potential is slightly lower, and TCP flow control signalling is
properly utilized.

The kernel will queue data into the socket buffer, then signal the
remote peer to stop sending data, until we resume reading again.
Some fixes to CNetMessage processing

* Change CNode::vRecvMsg to be a deque instead of a vector (less copying)
* Make sure to acquire cs_vRecvMsg in CNode::CloseSocketDisconnect (as it
  may be called without that lock).
Use per-message send buffer, rather than per connection
Bitcoin-Qt: ensure createTrayIconMenu() is always called on Mac

- this should prevent GUI issues on Mac that were observed before (disappearing
  GUI - see #1522)
- the patch ensures, that createTrayIconMenu() is always called on Mac to
  process and use our MacDockIconHandler
Process getdata invs separately until send buffer overflows

There exists a per-message-processed send buffer overflow protection,
where processing is halted when the send buffer is larger than the
allowed maximum.

This protection does not apply to individual items, however, and
getdata has the potential for causing large amounts of data to be
sent. In case several hundreds of blocks are requested in one getdata,
the send buffer can easily grow 50 megabytes above the send buffer
limit.

This commit breaks up the processing of getdata requests, remembering
them inside a CNode when too many are requested at once.
Merge pull request #2409 from sipa/txoptim

Network optimalizations
Merge pull request #2422 from sipa/nowalcache

Don't use -dbcache for BDB anymore
Merge pull request #2361 from L2G/font-tweak

Clean up font size in main window for observed inconsistency in Mac OS
Merge pull request #2386 from Diapolo/Mac_GUI

Bitcoin-Qt: ensure createTrayIconMenu() is always called on Mac
Words in English language are more short than in other langs usually.
Tabs don't fits in line in Spanish/German/Russian when they has two words.
Wallet has limited functionality. It can send & receive coins. So we can
safely rename "Send coins" to "Send" and "Receive coins" to "Receive".
Address book is just stored addresses.