#2132 - lint and fix with ale#command#Run

A new function is added here which will later be modified for public use
in linter and fixer callbacks. All linting and fixing now goes through
this new function, to prove that it works in all cases.

test/test_highlight_placement.vader

@@ -9,6 +9,7 @@ Before:
   Save g:ale_set_signs
 
   let g:ale_run_synchronously = 1
+  unlet! g:ale_run_synchronously_callbacks
   let g:ale_set_highlights = 1
   let g:ale_set_signs = 1
   let g:ale_buffer_info = {}
@@ -64,6 +65,7 @@ Before:
 After:
   Restore
 
+  unlet! g:ale_run_synchronously_callbacks
   unlet! g:items
   unlet! b:ale_enabled
 
@@ -81,6 +83,7 @@ Given testft(A Javscript file with warnings/errors):
 
 Execute(Highlights should be set when a linter runs):
   ALELint
+  call ale#test#FlushJobs()
 
   AssertEqual
   \ [