Include leading / in buffer().rev()

Slowly pave the way for relative paths.

plugin/fugitive.vim

@@ -65,7 +65,7 @@ function! s:shellslash(path)
 endfunction
 
 function! s:recall()
-  let rev = s:buffer().rev()
+  let rev = s:sub(s:buffer().rev(), '^/', '')
   if rev ==# ':'
     return matchstr(getline('.'),'^#\t\%([[:alpha:] ]\+: *\)\=\zs.\{-\}\ze\%( (new commits)\)\=$\|^\d\{6} \x\{40\} \d\t\zs.*')
   endif
@@ -497,7 +497,7 @@ function! s:buffer_rev() dict abort
   elseif self.spec() =~ '\.git/refs/\|\.git/.*HEAD$'
     return self.spec()[strlen(self.repo().dir())+1 : -1]
   else
-    return self.path()
+    return self.path('/')
   endif
 endfunction