Importprivkey shows address
Scratching an itch: make `importprivkey` output the corresponding address.
Without this PR, `importprivkey` shows no output. Because we're moving towards an "address-based" RPC interface, rather than "account-based", there's a gap when using `importprivkey` because there's no way to assign it to a specific account, but also no easy way to determine the address. This change fixes that wart.
Fetch params from ipfs if possible
This patch allows fetch-params to download the params from [ipfs], if it's installed. This reduces the need for a central server and ensures the params are available if the official server ceases to exist.
For now, the default is still wget. If wget exits with an error, the script automatically tries ipfs. To use ipfs instead of wget:
ZC_DISABLE_WGET=1 ./zcutil/fetch-params.sh
[ipfs]: https://github.com/ipfs/go-ipfs
Fixes for gcc 7
This fixes a few issues when using a newer compiler (in my case gcc 7.1.1) available in for example Arch Linux.
Solves for example this issue: https://github.com/zcash/zcash/issues/2304
The first thing is an error when checking for boost_system and is solved by disabling that warning (wich is treated as an error and, hence, stops the build):
```
configure:22242: checking for exit in -lboost_system-mt
configure:22267: g++ -m64 -o conftest -std=c++11 -pipe -fPIC -O1 -fwrapv -fno-strict-aliasing -Werror -g -Wformat -Wformat-security -Wstack-protector -fstack-protector-all -fPIE ..<snip>... /x86_64-unknown-linux-gnu/share/../lib conftest.cpp -lboost_system-mt -lanl >&5
conftest.cpp:70:6: error: declaration of 'char exit()' conflicts with built-in declaration 'void exit(int)' [-Werror=builtin-declaration-mismatch]
char exit ();
^~~~
cc1plus: all warnings being treated as errors
```
The second thing was to clean some code that is deprecated in C++11 which also lead to a warning treated as error. It could also be fixed with `-Wno-deprecated` but better to fix the issue in my opinion.
