patch 8.0.0615: using % with :hardcopy wrongly escapes spaces

Problem:    Using % with :hardcopy wrongly escapes spaces. (Alexey Muranov)
Solution:   Expand % differently. (Christian Brabandt, closes #1682)

src/testdir/test_hardcopy.vim

@@ -60,3 +60,12 @@ func Test_with_syntax()
     set printoptions&
   endif
 endfunc
+
+func Test_fname_with_spaces()
+  split t\ e\ s\ t.txt
+  call setline(1, ['just', 'some', 'text'])
+  hardcopy > %.ps
+  call assert_true(filereadable('t e s t.txt.ps'))
+  call delete('t e s t.txt.ps')
+  bwipe!
+endfunc