Fix broken functional test.

In Lua, all math is floating point.  We need to coerce the result of a
division into a integer with the `{get,set}_height` and
`{get,set}_width` window_spec functional tests.
build: print the error result when the tests fail

Any diagnostic information is useful when things fail.  In my case, it
printed out the fact that the tests were segfaulting.
deps: Update bundled lua client version

The new version fixes defunct processes which causes random test failures on
some systems(#1519)
Merge PR #1547 'Update bundled lua client version'
Add missing refcount increment for systemlist()

- get_system_output_as_rettv() was missing a refcount increment when
  returning an empty list, i.e. when there was no output
- we now use rettv_list_aloc() instead of list_alloc()
- issue #1530
Merge pull request #1552 from equalsraf/tb-fix-1530

add missing refcount increment for systemlist()
build: allow skipping of the hash check in the download step

This is useful when trying to bisect an issue in a dependency, and we
want to pull from a specific commit but don't want to have to download
and determine the sha1sum and md5sum of the tarball.
Merge pull request #1543 from jszakmeister/fix-broken-functional-tests

Fix broken functional test.
build: add failure message along with number in GenerateHelptags.cmake
Merge pull request #1544 from jszakmeister/run-tests-error-code

build: print the error result when the tests fail
build: probe the compiler to see if we need to turn down _FORTIFY_SOURCE

Some builds don't use Release (such as Gentoo, though it can be told
to).  So let's go a bit further and probe the compiler to see if we need
to turn down the _FORTIFY_SOURCE level.
Fix outdated msgpack-rpc doc.

Needed after neovim/python-client#58.
Merge pull request #1514 from jszakmeister/better-fortify-detection

build: probe the compiler to see if we need to turn down _FORTIFY_SOURCE
Improve Python host messages.
Merge pull request #1559 from fwalch/python-messages

Improve Python host messages.
Avoid printing an error response when detecting xclip.

While we're at, using the slightly more portable `command -v` technique
to detect the executable.  Also, there's no need to use `io.popen()` if
we aren't going to record the path.  Instead, let's use the simpler
`os.execute()` to detect the presence of xclip.
Merge pull request #1554 from jszakmeister/allow-skipping-of-sum

build: allow skipping of the hash check in the download step
Merge pull request #1556 from elmart/fix-msgpack-rpc-docs

Fix outdated msgpack-rpc doc.
Merge pull request #1555 from jszakmeister/silent-xclip-find-executable

Avoid printing an error response when detecting xclip.
Add Boolean argument escape_csi to vim_feedkeys

- By default vim_feedkeys escaped all input for CSI/K_SPECIAL bytes
  before using it. However since vim_replace_termcodes() also escapes
  the input string chaining these functions together escapes input twice
- vim_feedkeys() now takes a third Boolean argument to enable/disable
  escaping
- Breaks API compatibility