The new oldtest directory is in test/old/testdir. The reason for this is
that many tests have hardcoded the parent directory name to be
'testdir'.

This is a port of these two patches combined:

vim-patch:8.1.1524: tests are silently skipped

Problem:    Tests are silently skipped.
Solution:   Throw an exception for skipped tests in more places.
https://github.com/vim/vim/commit/b0f94c1ff34d27d33aa9f96204985ea29c2eb0a1

vim-patch:8.1.1544: some balloon tests don't run when they can

Problem:    Some balloon tests don't run when they can.
Solution:   Split GUI balloon tests off into a separate file. (Ozaki Kiichi,
            closes vim/vim#4538)  Change the feature check into a command for
            consistency.
https://github.com/vim/vim/commit/b46fecd3454399f8ebdc5055302e4bfc5a10f98b

Omit test_lua.vim: previous patches are N/A
Omit test_memory_usage.vim: previous patches are N/A
Omit test_textprop.vim: previous patches are N/A
Omit test_winbar.vim: previous patches are N/A
Omit test_termcodes.vim: mostly N/A
Skip Test_mouse_positon() because it uses test_setmouse().
Cannot throw error in a Test_nocatch_ test.
Use latest `CheckFeature clipboard_working` for test_quotestar.vim

Problem:    More functions can be used as methods.
Solution:   Make various functions usable as a method.
https://github.com/vim/vim/commit/3f4f3d8e7e6fc0494d00cfb75669a554c8e67c8b

test_prompt_buffer.vim already had all the changes, except
Test_prompt_garbage_collect().

Problem:    Test88 is old style.
Solution:   Turn into a new style test. (Yegappan Lakshmanan, closes vim/vim#5347)
https://github.com/vim/vim/commit/213ed008bbcd9fe0d3329b17f5f4af0169e448ff

'test_conceal.vim' requires +conceal and +terminal so it is N/A.

Problem:    Error for Python exception does not show useful info.
Solution:   Show the last line instead of the first one. (Ben Jackson,
            closes vim/vim#4381)
https://github.com/vim/vim/commit/7f3a28490abb7c495239fc438825e3d1aaafa76d

Problem:    Using :python sets 'pyxversion' even when not executed.
Solution:   Check the "skip" flag. (Shane Harper, closes vim/vim#3995)
https://github.com/vim/vim/commit/14816ad6e58336773443f5ee2e4aa9e384af65d2

Problem:    Preferred cursor column not set in interfaces.
Solution:   Set w_set_curswant when setting the cursor. (David Hotham,
            closes vim/vim#3060)
https://github.com/vim/vim/commit/53901442f37a59e5495165f91db5574c0b43ab04

Problem:    Python test doesn't wipe out hidden buffer.
Solution:   Wipe out the buffer. (Ben Jackson, closes vim/vim#4189)
https://github.com/vim/vim/commit/bfd36036700ab2d4c9de48e37f222f4a4dd7b3b0

Problem:    E315 ml_get error when using Python and hidden buffer.
Solution:   Make sure the cursor position is valid. (Ben Jackson,
            closes vim/vim#4153, closes vim/vim#4154)
https://github.com/vim/vim/commit/63dbfd33c1d47400c62775842b5b750ee69e2383