Reduce boost namespace pollution

[theuni]

Should fix #3483, as well as being a good practice in general. The second commit changes a bit of code, so it's not lumped in with the rest. The others should be semantic changes only.

After this, there are only 2 users of "using namespace boost::foo" left, and those were left in because they're very wordy otherwise.

[zander]

I really like the first and the last commit, they look good to me. I personally would reject the middle commit that touches the unit test (see comment there).

[jonasschnelli]

IMO: this makes the code more readable and i also see this as a good practice.
ACK (reviewed, compiled, make check).

[laanwj]

Looks good to me. I'm not a big fan of 'using namespace XXX' on a global level either. If it makes things too wordy you can always use them at a function level.

Needs rebase though.

[theuni]

rebased

[sipa]

Untested ACK.

@zander Your comment on the second commit is lost due to the rebase.

[theuni]

Pre-rebase comments can be seen here:
theuni@705292e#commitcomment-9105866

[laanwj]

ACK, no binary changes in bitcoind

230b275c285433955d58623a3d388f7b89839003c359773876932a5cb7686a5e  bitcoind.856e862.stripped
230b275c285433955d58623a3d388f7b89839003c359773876932a5cb7686a5e  bitcoind.f55c5e9.stripped