* vim-patch:8.0.0474: the client-server feature is not tested

Problem:    The client-server feature is not tested.
Solution:   Add a test.
https://github.com/vim/vim/commit/15bf76d40be1f1622ff5cc16596c308e76e2ca94

* vim-patch:8.0.0475: not enough testing for the client-server feature

Problem:    Not enough testing for the client-server feature.
Solution:   Add more tests.  Add the remote_startserver() function.  Fix that
            a locally evaluated expression uses function-local variables.
https://github.com/vim/vim/commit/7416f3e73ab2c4e7ae3adc2ff6e70234f7d40d2e

* vim-patch:8.0.0492: a failing client-server request can make Vim hang

Problem:    A failing client-server request can make Vim hang.
Solution:   Add a timeout argument to functions that wait.
https://github.com/vim/vim/commit/81b9d0bd5c705815e903e671e81b0b05828efd9c

Include src/nvim/testdir/test_clientserver.vim changes from
patches 8.0.0477, 8.0.0479.

* vim-patch:8.0.0633: the client-server test is still a bit flaky

Problem:    The client-server test is still a bit flaky.
Solution:   Wait a bit for the GUI to start.  Check that the version number
            can be obtained.
https://github.com/vim/vim/commit/60964f68740b8abcbb2d3f0f3aeade21d1bacb22

Include src/nvim/testdir/test_clientserver.vim changes
from patches 8.0.0507, 8.0.0511.

* vim-patch:8.0.1251: invalid expressin passed to WaitFor()

Problem:    Invalid expressin passed to WaitFor().
Solution:   Check if the variable exists.
https://github.com/vim/vim/commit/d97fbf171ec0e63117813da045d2a1c51a9b6f62

Problem:    Wordcount test is old style.
Solution:   Change into a new style test. (Yegappan Lakshmanan, closes vim/vim#2434)
https://github.com/vim/vim/commit/a703aaee4d6230ed81469ef0cb37f331bf255136

Problem:    Still too many old style tests.
Solution:   Convert a few more tests to new style. (Yegappan Lakshmanan,
            closes vim/vim#2272)
https://github.com/vim/vim/commit/430dc5d360166ca5bb6a73f2c87ae53e09282ecb

Skip Test_tag_file_encoding.
083_tag_search_with_file_encoding_spec.lua handles the same test case.

Problem:    May get ml_get error when :pydo deletes lines or switches to
            another buffer. (Nikolai Pavlov, issue vim/vim#1421)
Solution:   Check the buffer and line every time.
https://github.com/vim/vim/commit/a58883b4ea0bbb813fd4dd7eb49dd6f03e3e5387

(We only include the tests, the Vim code changes are N/A for Nvim.)

Vim doesn't test it on Windows.
See https://github.com/vim/vim/blob/master/src/testdir/Make_all.mak

Also removes `-` before `rm -rf` as `-f` is supposed to already suppress error.

Reasoning:

- No need to check for terminal size.
- No need to mess with terminal title.
- Allows old tests to timeout with the rest of the build proceeding.
- Less and less messy output to travis log.
- Opens a path allowing old tests run in parallel. Though last bit needs test
  refactoring.