parse out submodule path when not in a .git directory (#273).

autoload/airline/extensions/branch.vim

@@ -41,10 +41,18 @@ function! s:check_in_path()
     let root = get(b:, 'git_dir', get(b:, 'mercurial_dir', ''))
     let bufferpath = resolve(fnamemodify(expand('%'), ':p:h'))
 
-    " .git may be a repo or a file depending on the version of git for submodules
-    if !filereadable(root)
-      let root = expand(fnamemodify(root, ':h'))
+    if !filereadable(root) "not a file
+      " if .git is a directory, it's the old submodule format
+      if match(root, '\.git$') >= 0
+        let root = expand(fnamemodify(root, ':h'))
+      else
+        " else it's the newer format, and we need to guesstimate
+        let pattern = '\.git\(\\\|\/\)modules\(\\\|\/\)'
+        if match(root, pattern) >= 0
+          let root = substitute(root, pattern, '', '')
+        endif
     endif
+
     let b:airline_file_in_root = stridx(bufferpath, root) > -1
   endif
   return b:airline_file_in_root