Add 'includeexpr' and 'suffixesadd' to Sass

ftplugin/sass.vim

@@ -8,10 +8,12 @@ if exists("b:did_ftplugin")
 endif
 let b:did_ftplugin = 1
 
-let b:undo_ftplugin = "setl cms< inc< ofu<"
+let b:undo_ftplugin = "setl cms< inc< inex< ofu< sua<"
 
 setlocal commentstring=//\ %s
+setlocal includeexpr=substitute(v:fname,'\\%(.*/\\\|^\\)\\zs','_','')
 setlocal omnifunc=csscomplete#CompleteCSS
+setlocal suffixesadd=.css,.sass,.scss
 
 let &l:include = '^\s*@import\s\+\%(url(\)\=["'']\='