clear history when using clear button in RPC console

- current code does not clear history, when using the clear button, this
  is added
- remove a currently unused variable but add a TODO comment
remove "checkorder" and "reply" P2P commands

These command are a leftover from send-to-IP transactions, which have been
removed a long time ago.
Also removes CNode::mapRequests and CNode::PushRequests, as these were
only used for the mentioned commands.
make optionsmodel query real proxy state for ::data()

- don't rely on the QSettings for cases ProxyUse and ProxySocksVersion and
  query the real values via the GetProxy() call
- add a missing "succesful =" for case ProxyUse in ::setData()
Bitcoin-Qt: add new GCC compiler hardening options

- this patch enables several new GCC compiler hardening options that
  allows us to increase the security of our binaries (see:
  https://wiki.debian.org/Hardening)

-D_FORTIFY_SOURCE=2:
Enables compile-time protection against static sized buffer overflows.

-Wl,-z,relro -Wl,-z,now:
Enables full RELRO (RELocation Read-Only), which is a generic mitigation
technique to harden the data sections of an ELF binary/process. See:
http://isisblogs.poly.edu/2011/06/01/relro-relocation-read-only/ for
further details.
Bitcoin-Qt: remove unneeded "--param ssp-buffer-size=1" flag

- that flag is not needed when using "-fstack-protector-all", so remove it
  (see:
  http://stackoverflow.com/questions/1629685/when-and-how-to-use-gccs-stack-protection-feature)
Added script that verifies authenticity of binaries on SourceForge
Bugfix: do not mark all future coins spent
fix a double inclusion of txdb.h in bitcoin-qt.pro
Fixed compile error on FreeBSD 9.
See http://code.google.com/p/leveldb/issues/detail?id=98
Fixed 100% CPU utilization problem on FreeBSD 9
Bugfix: off-by-one error in coinbase maturity check
Bugfix: add missing fee check
Bugfix: off-by-one in priority calculation
Added some comments

Some clarifications after a code review by Mike Hearn.
Bugfix: actually use CCoinsViewMemPool
Fixes a race condition in CreateNewBlock and a future null deref on testnet.

CreateNewBlock was reading pindexBest at the start before taking the lock
so it was possible to have the the block content not match the prevheader
and this can also trigger a newly added assert in ConnectBlock.

I noticed this during a code review after twobitcoins reported that ab91bf39
(BIP30 for all blocks) could cause a null dereference on a modified node
that mined during the IBD, or on testnet when it reached heights 91842 and
91880 due to CreateNewBlock calling ConnectBlock with pindex->phashBlock NULL.
Fix out-of-bounds read noticed by Ricardo Correia

Sizeof() returned the size of a pointer instead of the size of the buffer.
Fixes issue #1924.
Don't force getblocktemplate to have a parameter.

This looks like it was just a munged merge when ultraprune
was committed.
Show warning when using prerelease version

Implements #1948

- Add macro `CLIENT_VERSION_IS_RELEASE` to clientversion.h
- When running a prerelease (the above macro is `false`):
  - In UI, show an orange warning bar at the top. This will be used for other
    warnings (and alerts) as well, instead of the status bar.
  - For `bitcoind`, show the warning in the "errors" field in `getinfo`
    response.
ensure AskPassphraseDialog::eventFilter forwards events

- instead of "return false;" use "return QDialog::eventFilter(object,
  event);" to harmonize this event filter with our default behaviour
- remove orphan spaces found while editting the files