async: rename variable

rename g:airline#init#async variable to g:airline#init#vim_async
because that is what it is for: showing whether vim supports async. Is
not set vor nvim, because nvim always supports jobs.

autoload/airline/extensions/branch.vim

@@ -125,7 +125,7 @@ function! s:update_hg_branch(...)
     let cmd='LC_ALL=C hg qtop'
     let stl=lawrencium#statusline()
     if !empty(stl) && get(b:, 'airline_do_mq_check', 1)
-      if g:airline#init#async
+      if g:airline#init#vim_async
         call airline#async#get_mq_async(cmd, expand('%:p'))
       elseif has("nvim")
         call airline#async#nvim_get_mq_async(cmd, expand('%:p'))
@@ -200,7 +200,7 @@ function! s:update_untracked()
 
   for vcs in keys(s:vcs_config)
     let config = s:vcs_config[vcs]
-    if g:airline#init#async
+    if g:airline#init#vim_async
       " Note that asynchronous update updates s:vcs_config only, and only
       " s:update_untracked updates b:buffer_vcs_config. If s:vcs_config is
       " invalidated again before s:update_untracked is called, then we lose the
@@ -308,7 +308,7 @@ endfunction
 
 function! s:reset_untracked_cache(shellcmdpost)
   " shellcmdpost - whether function was called as a result of ShellCmdPost hook
-  if !g:airline#init#async && !has('nvim')
+  if !g:airline#init#vim_async && !has('nvim')
     if a:shellcmdpost
       " Clear cache only if there was no error or the script uses an
       " asynchronous interface. Otherwise, cache clearing would overwrite

autoload/airline/extensions/po.vim

@@ -25,7 +25,7 @@ function! airline#extensions#po#stats()
   endif
 
   let cmd = 'msgfmt --statistics -o /dev/null -- '
-  if g:airline#init#async
+  if g:airline#init#vim_async
     call airline#async#get_msgfmt_stat(cmd, expand('%:p'))
   elseif has("nvim")
     call airline#async#nvim_get_msgfmt_stat(cmd, expand('%:p'))

autoload/airline/init.vim

@@ -18,7 +18,7 @@ function! airline#init#bootstrap()
 
   let g:airline#init#bootstrapping = 1
 
-  let g:airline#init#async = (v:version >= 800 && has('job'))
+  let g:airline#init#vim_async = (v:version >= 800 && has('job'))
   let g:airline#init#is_windows = has('win32') || has('win64')
 
   call s:check_defined('g:airline_detect_modified', 1)