Allow -onlynet=onion to be used

Just an alias for onlynet=tor, but matches the new name
of the proxy option -onion= better.
Add IsReachable(net) function

Allows other parts of the program to query for reachable
status of a network. Similar to IsLimited(net).
Add GetNetworkName function

Returns the network name for an Network enum.
[Qt] move SubstituteFonts() above ToolTipToRichTextFilter

- doesn't belong to the ToolTipToRichTextFilter class so move it up
Add a way to limit deserialized string lengths

and use it for most strings being serialized.
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.
Merge pull request #4682

c33b983 Don't poll showmyip.com, it doesn't exist anymore (Wladimir J. van der Laan)
Reapply: Reject transactions with excessive numbers of sigops

Reverting was based on a misunderstanding, it appears.

Github-Pull: #4150
bitcoin-tx: fix build warnings

Cleans up a bunch of:
warning: missing braces around initializer for ‘const<anonymous struct>’
Merge pull request #4696

616c243 bitcoin-tx: fix build warnings (Cory Fields)
Merge pull request #4659

c4bae53 [Qt] move SubstituteFonts() above ToolTipToRichTextFilter (Philip Kaufmann)
Closely track mempool byte total. Add "getmempoolinfo" RPC.

Goal:  Gain live insight into the mempool.  Groundwork for future work
that caps mempool size.
build: fix automake warnings about the use of INCLUDES

While we're at it, reduce the use of LIBS as well. This makes dependencies
explicit.

Fixes building with (the not-yet-merged) libsecp256k1 as well.

Github-Pull: #4689
Rebased-By: Wladimir J. van der laan <laanwj@gmail.com>
Rebased-From: 909b347 c0e5dda
Merge pull request #4638

6f2c26a Closely track mempool byte total. Add "getmempoolinfo" RPC. (Jeff Garzik)
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.

Should close #3219.
build: add option for reducing exports

Enabled automatically if boost >= 1.49.
See: https://svn.boost.org/trac/boost/ticket/2309

Also, check for a default visibility attribute, so that we can mark future
api functions correctly.
build : fix CPPFLAGS for libbitcoin_cli
depends: fix shasum on osx < 10.9

Shasum verification from stdin doesn't work there, so we write to a file
instead.

Formatted a bit too.
build: add funcs.mk to the list of meta-depends

If anything in funcs.mk changes, everything must rebuild
tests: fix test-runner for osx. Closes ##4708

Use the more portable $$ rather than $BASHPID