The included `vimrc` file sets mappings for <ScrollWheelUp> and
<ScrollWheelDown>, so that scrolling is smooth. Unfortunately,
'compatible' is set by default [0], so the `<>` notation used for those
mappings isn't enabled. Instead of the key `<ScrollWheelUp>` being
mapped, the mapping is actually from the typed string "<ScrollWheelUp>".
[0]: `:help compatible-default` explains that vim will turn the
'compatible' option off when "a user vimrc is found", or under various
other conditions (note that the system-wide vimrc doesn't count [1]),
but even in the case where a user vimrc exists, this system-wide vimrc
is executed before that happens.
[1]: From `:help compatible-default`:
Note that this does NOT happen when a system-wide vimrc file was
found.
The mouse=a was removed after updating to vim 8 as vim by default
now sets mouse=a. But this only works if no ~/.vimrc is found - if
there is one then mouse won't be set. As we really want mouse=a on
Termux since it is that useful on touch screens we enable it again
regardless if there is a ~/.vimrc or not.
Fixes#912.
