Update UNIX build docs

Add version numbers to UNIX build documentation, and remove misplaced "Ubuntu" heading.
Don't poll showmyip.com, it doesn't exist anymore

Fixes #4679.

This leaves us with only one candidate, checkip.dyndns.org.
GetMyExternalIP should be phased out as soon as possible.

Rebased-From: c33b983
Avoid querying DNS seeds, if we have open connections.

The goal is to increase independence and privacy.
In -? output: -keypool, -gen, -genproclimit depend on ENABLE_WALLET

Rebased-From: a7e1d50
Clarify that redeemScript is often optional

Rebased-From: 6265ecc
Ignore too-long redeemScripts while loading wallet

This avoids that long redeemScripts that were grandfathered in
prevent the wallet from loading.

Fixes #4313.

Rebased-From: 18116b0
Modified comment to make it clear that pull request refers to Bitcoin Core.
qt: fix 'opens in testnet mode when presented with a BIP-72 link with no fallback'

Passes tests:

```
$ ./bitcoin-qt 'bitcoin:?r=http://www.example.com/'
.. fixed the original problem - this launches mainnet.

$ ./bitcoin-qt 'bitcoin:mngeNQbTKnmaMbx8EXCYdwUbnt9JJD52cC'
.. launches testnet

$ ./bitcoin-qt -testnet 'bitcoin:1NXXeQRyMFFFRfyUix2o7mk1vhvk2Nxp78'
.. sanity check - launches mainnet.
```

Fixes #4355. Closes #4411.

Rebased-From: dd49e92
gitian: Bump miniupnp version to 1.9.20140701

Also change build system: STATICLIB is now MINIUPNP_STATICLIB.
base58: add paranoid return value checks

Rebased-From: 88df548
Update addressbookpage.cpp
Update coincontroldialog.ui
Update optionsdialog.ui
Update bitcoingui.cpp
l10n Update and add strings against bitcoin_en.ts
Avoid a segfault on getblock if it can't read a block from disk.

Rebased-From: 954d2e7
Update Debian packaging description for new bitcoin-cli
build: Fix boost build on some platforms

When the libpath doesn't line up with the value from config.sub, we don't find
the correct path to boost's libs. This adds a hack to try another path before
giving up.
build: fix FDELT_TYPE configure check

This probably never worked properly. Confirmed working now with every compiler
I throw at it.

Rebased-From: 8021cf8
AvailableCoins: acquire cs_main mutex

It's required when called from WalletModel

Rebased-From: ea3acaf