Problem:    Reloading a script gives errors for existing functions.
Solution:   Allow redefining a function once when reloading a script.
https://github.com/vim/vim/commit/ded5f1bed7ff2d138b3ee0f9610d17290b62692d

Problem:    Cannot get the script line number when executing a function.
Solution:   Store the line number besides the script ID. (Ozaki Kiichi,
            closes vim/vim#3362)  Also display the line number with ":verbose set".
https://github.com/vim/vim/commit/f29c1c6aa3f365c025890fab5fb9efbe88eb1761

- Re-enable Test_BufLeave_Wipe. 66f5e5c7d7ce

This is my (probably-wrong) application of Zyx's suggestion in #9163:

> free_buffer_stuff() already removes changedtick. It is better to
> make `free_options` a flag variable and avoid calling
> buf_init_changedtick() based on some flag there: current workflow
> looks weird as it first removes `b:changedtick`, then re-adds it
> by calling buf_init_changedtick(), then remove again.

> Also based on my understanding it looks logical to not remove
> `b:changedtick`, but to *replace* it with something allocated if
> needed based on examining reference count before calling
> `unref_var_dict`. Because now you have key disappearing from
> dictionary for no good reason.

Patch-By: Nikolai Aleksandrovich Pavlov <kp-pav@yandex.ru>

Problem:    Floating point exception with "%= 0" and "/= 0".
Solution:   Avoid dividing by zero. (Dominique Pelle, closes vim/vim#4058)
https://github.com/vim/vim/commit/e21c1580b7acb598a6e3c38565434fe5d0e2ad7a

Despite the PVS warning, we do not want to conflate these
cases, they are semantically different.

Problem:    Lock flag in new dictitem is reset in many places.
Solution:   Always reset the lock flag.
https://github.com/vim/vim/commit/c89d4b35300b98cf68b14c89c8e1add51bd857e3

Problem:    ":profdel func" does not work if func was called already.
            (Dominique Pelle)
Solution:   Reset uf_profiling and add a flag to indicate initialization was
            done.
https://github.com/vim/vim/commit/ad6480961080f80a455b2394f27b02935a2ded52

Problem:    Incomplete set of assignment operators.
Solution:   Add /=, *= and %=. (Ozaki Kiichi, closes vim/vim#3931)
https://github.com/vim/vim/commit/ff697e6cef8ced7717a21fd525ab3200b2f1724f

Problem:    swapinfo() leaks memory.
Solution:   Avoid allocating the strings twice.
https://github.com/vim/vim/commit/e6fdf79980c0f2856700d4f46de700293f477429