Wallet API: add some missing override keyword

[stoffu]

Also remove dust() from UnsignedTransactionImpl (already in PendingTransactionImpl)

[moneromooo-monero]

That's a bit spammy, no ?

[stoffu]

Well, this patch was motivated by more than 4000 lines of warning like below:

[ 90%] Building CXX object src/wallet/api/CMakeFiles/obj_wallet_api.dir/wallet.cpp.o
In file included from /Users/stoffu/monero/src/wallet/api/wallet.cpp:32:
/Users/stoffu/monero/src/wallet/api/wallet.h:59:10: warning: 'createWatchOnly' overrides a member function but is not marked
      'override' [-Winconsistent-missing-override]
    bool createWatchOnly(const std::string &path, const std::string &password,
         ^
/Users/stoffu/monero/src/wallet/api/wallet2_api.h:490:18: note: overridden virtual function is here
    virtual bool createWatchOnly(const std::string &path, const std::string &password, const std::string &language) const = 0;
                 ^

all coming from src/wallet/api/wallet.cpp. Full set: https://paste.fedoraproject.org/paste/4Jy5ph89hETLaIC-fl5suA

They seem to be caused by some of the overridden functions in WalletImpl being supplied with the override keyword while others not (the other classes don't have any functions with override and thus don't generate the warnings). However, I noticed that I don't observe this behavior on other platforms. I also don't see it on the logs of the buildbot's OSX builds. Is it just me seeing these warnings?

I'm on macOS Sierra 10.12.6 (16G1408). The compiler version is:

Apple LLVM version 9.0.0 (clang-900.0.39.2)
Target: x86_64-apple-darwin16.7.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin

[moneromooo-monero]

This "use it once, use it always" kinda rings a bell, I believe we had this problem earlier with ledger. Alright then, let it go in.

Are you using CLANG by any chance ? I seem to be remembering something to do with it...

[stoffu]

I think I'm using CLANG because that's the default for OSX and I didn't do anything particular to install GCC.

From CMakeCache.txt:

CMAKE_CXX_COMPILER:FILEPATH=/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++
CMAKE_C_COMPILER:FILEPATH=/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/cc