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.
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Fix outdated msgpack-rpc doc.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Fix outdated msgpack-rpc doc.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
Functional tests for feedkeys CSI escaping

- tests for vim_feedkeys and replace_termcodes