Fix substitute newline: Memory functions: Improve style.

`try_malloc` was changed in 8bb2c2c0742c57150655e18cf8418a758cebdce8 to
avoid a warning when size is 0. Then, this improves some things on that:

- Use local vars instead of changing parameters.
- Homogenize style for other related functions.
Merge pull request #1526 from elmart/mem-func-impr

Memory functions: Improve style.
Print an error and exit when there are no plugins.

Issue: #1537

Running the :UpdateRemotePlugins command will show an ugly, unhelpful
error when no plugins were found. This change has neovim print an error message
and does not attempt to start the python-client which requires at least one
plugin.
Merge pull request #1539 from Floobits/master

Print an error and exit when there are no plugins.
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()
clipboard: support separate '+' and '*' clipboards
clipboard: handle linewise/charwise selections correctly
RFC: systemlist: keep final newline
clipboard: clean up unnamedclip logic
change option "unnamedclip" back to "clipboard=unnamed/unnamedplus"

This allows to configure which of '*' and '+' should be used for
the unnamed clipboard
clipboard: add functional test
clipboard: fix `let @+ = ...` and add test