branch: disable FocusGained handler when updating fugitive information

closes #2029

autoload/airline/extensions/branch.vim

@@ -112,6 +112,9 @@ function! s:update_git_branch()
 endfunction
 
 function! s:display_git_branch()
+  " disable FocusGained autocommand, might cause loops because system() causes
+  " a refresh, which causes a system() command again #2029
+  call airline#util#focusgain(0)
   let name = b:buffer_vcs_config['git'].branch
   try
     let commit = matchstr(FugitiveParse()[0], '^\x\+')
@@ -128,7 +131,7 @@ function! s:display_git_branch()
     endif
   catch
   endtry
-
+  call airline#util#focusgain(1)
   return name
 endfunction
 

autoload/airline/util.vim

@@ -11,6 +11,7 @@ let s:spc = g:airline_symbols.space
 let s:nomodeline = (v:version > 703 || (v:version == 703 && has("patch438"))) ? '<nomodeline>' : ''
 let s:has_strchars = exists('*strchars')
 let s:has_strcharpart = exists('*strcharpart')
+let s:focusgained_enabled = 0
 
 " TODO: Try to cache winwidth(0) function
 " e.g. store winwidth per window and access that, only update it, if the size
@@ -190,3 +191,11 @@ function! airline#util#stl_disabled(winnr)
    \ airline#util#getwinvar(a:winnr, 'airline_disabled', 0) ||
    \ airline#util#getbufvar(winbufnr(a:winnr), 'airline_disable_statusline', 0)
 endfunction
+
+function! airline#util#focusgain(allow)
+  let s:focusgained_enabled = a:allow
+endfunction
+
+function! airline#util#focusgained_disabled()
+  return s:focusgained_enabled < 1
+endfunction