don't use sed's -i option to stay posix compliant

POSIX does not define sed's -i option. To stay as portable
as possible we should not relay on it.
doc: remove specific mention of boost 1.55

There is no need to use any specific version of boost on Linux/Unix.
Even 1.37 should still work.

Also the mention of boost-dev doesn't belong after adding oldstable.
Remove it. libboost-all-dev is already mentioned earlier.
Merge pull request #4120

dbe8f75 don't use sed's -i option to stay posix compliant (Fabian Raetz)
rpc: add `getblockchaininfo` and `getnetworkinfo`

Adds two new info query commands that take over information from
hodge-podge `getinfo`.

Also some new information is added:
- `getblockchaininfo`
  - `chain`: (string) current chain (main, testnet3, regtest)
  - `verificationprogress: (numeric) estimated verification progress
  - `chainwork`
- `getnetworkinfo`
  - `localaddresses`: (array) local addresses, from mapLocalHost (fixes #1734)
qt: periodic translations update
Merge pull request #4127

d387b8e rpc: add `getblockchaininfo` and `getnetworkinfo` (Wladimir J. van der Laan)
build: fix make clean on OSX

Rebased-From: 74df0f5
Rebased-By: Wladimir J. van der Laan <laanwj@gmail.com>
ui: Check for !pixmap() before trying to export QR code

Adds null pointer checks as well as prevents the Save/Copy context
menu from appearing at all if no image is shown.

Fixes issue #4140
Add missing cs_main lock to VerifyDB

Fixes issue #4139.
[Qt] fix ugly typo in bitcoin.cpp

Closes #4145.

Rebased-By: Wladimir J. van der Laan <laanwj@gmail.com>
Rebased-From: 1e4b083
Merge pull request #4141

9d558e1 ui: Check for !pixmap() before trying to export QR code (Wladimir J. van der Laan)