Use Vim 8 features for updating the quickfix list without replacing quickfix lists from other plugins

[yegappan]

When the syntastic plugin is updating a quickifx list asynchronously, some other
Vim plugin or user can create/modify the quickfix list resulting in the syntastic
plugin updating the incorrect quickfix list. This can be avoided by using
the new features in Vim8.

Refer to the following thread for the steps to do this:
https://groups.google.com/forum/#!topic/vim_use/LTWNG0nRQCc

[lcd047]

Please refer to #699. New feature will be added health permitting, if / when I can get myself together to re-start working at syntastic. In the mean time you can:

1. submit working patches to add the features you want,
2. fork syntastic, or
3. use something else (ale seems to be a popular destination for syntastic refugees).

Sorry about that.