Write fee estimate and peers files only when initialized

Fixes #4669.

Move the loading of addresses to StartNode() to make it more
self-contained.
Reserve only one network specific cached path per session
Remove CBaseChainParams::NetworkID()
Use ModifyCoins instead of mutable GetCoins.

Replace the mutable non-copying GetCoins method with a ModifyCoins, which
returns an encapsulated iterator, so we can keep track of concurrent
modifications (as iterators can be invalidated by those) and run cleanup
code after a modification is finished.

This also removes the overloading of the 'GetCoins' name.
Get rid of CCoinsView's SetCoins and SetBestBlock.

All direct modifications are now done through ModifyCoins, and BatchWrite is
used for pushing batches of queued modifications up, so we don't need the
low-level SetCoins and SetBestBlock anymore in the top-level CCoinsView class.
Do not keep fully spent but unwritten CCoins entries cached.

Instead of storing CCoins entries directly in CCoinsMap, store a CCoinsCacheEntry
which additionally keeps track of whether a particular entry is:
* dirty: potentially different from its parent view.
* fresh: the parent view is known to not have a non-pruned version.

This allows us to skip non-dirty cache entries when pushing batches of changes up,
and to remove CCoins entries about transactions that are fully spent before the
parent cache learns about them.
Add coins_tests with a large randomized CCoinViewCache test.
Get rid of the dummy CCoinsViewCache constructor arg
qt: add proxy to options overridden if necessary.

If proxy is disabled in the gui but enabled via the command line, it needs to
be added to the override list.
fix a possible memory leak in CWalletDB::Recover

- convert pdbCopy into a boost::scoped_ptr to ensure memory gets freed
  in all cases (e.g. after "ret > 0")
fix possible memory leaks in CWallet::EncryptWallet

- add missing deletes for pwalletdbEncryption
- add an assert before trying to reserve memory for pwalletdbEncryption
- add a destructor to CWallet, which ensures deletion of
  pwalletdbEncryption on object destruction
change exit(1) to an assert in CWallet::EncryptWallet
update getnetworkinfo help with subversion

- add missing subversion field to getnetworkinfo help
- fix style and format errors in help string
- remove unneeded int casts
CBufferedFile: convert into a non-refcounted RAII wrapper

- it now takes over the passed file descriptor and closes it in the
  destructor
- this fixes a leak in LoadExternalBlockFile(), where an exception could
  cause the file to not getting closed

- disallow copies (like recently added for CAutoFile)
- make nType and nVersion private
CBufferedFile: add explicit close function

- also use identical close function for CAutoFile (avoids setting file to
  NULL under wrong conditions)
CAutoFile: make file private
Qt: allow "emergency" shutdown during startup

- allows closing our splash screen to abort startup
Fixed setaccount accepting foreign address

Fixed issue #4209 where using setaccount with a foreign
address causes the address to be added to your receiving addresses.
Changed mixed indentation to four spaces

Put `test/rpc_wallet_tests.cpp` through clang-format.
Merge pull request #4985

bc470c4 Changed mixed indentation to four spaces (Eric Shaw)
31d6390 Fixed setaccount accepting foreign address (Eric Shaw)