patch 8.1.1638: running tests leaves some files behind

Problem:    Running tests leaves some files behind.
Solution:   Delete the files. (Ozaki Kiichi, closes #4617)

src/testdir/test_functions.vim

@@ -1528,10 +1528,10 @@ func Test_bufadd_bufload()
   call assert_equal([''], getbufline(buf, 1, '$'))
 
   let curbuf = bufnr('')
-  call writefile(['some', 'text'], 'otherName')
+  call writefile(['some', 'text'], 'XotherName')
-  let buf = bufadd('otherName')
+  let buf = bufadd('XotherName')
   call assert_notequal(0, buf)
-  call assert_equal(1, bufexists('otherName'))
+  call assert_equal(1, bufexists('XotherName'))
   call assert_equal(0, getbufvar(buf, '&buflisted'))
   call assert_equal(0, bufloaded(buf))
   call bufload(buf)
@@ -1554,6 +1554,7 @@ func Test_bufadd_bufload()
   call assert_equal(0, bufexists(buf2))
 
   bwipe someName
-  bwipe otherName
+  bwipe XotherName
   call assert_equal(0, bufexists('someName'))
+  call delete('XotherName')
 endfunc

src/testdir/test_popupwin.vim

@@ -1708,6 +1708,7 @@ func Test_popupwin_with_buffer()
   let winid = popup_create(bufnr(''), {})
   redraw
   call popup_close(winid)
+  call delete('XsomeFile')
 endfunc
 
 func Test_popupwin_width()

src/version.c

@@ -777,6 +777,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1638,
 /**/
     1637,
 /**/