patch 8.1.2098: mksession test fails on MS-Windows

Problem:    mksession test fails on MS-Windows.
Solution:   Skip testing with backslashes on MS-Windows.

src/testdir/test_mksession.vim

@@ -565,6 +565,9 @@ endfunc
 
 " Test for changing backslash to forward slash in filenames
 func Test_mksession_slash()
+  if exists('+shellslash')
+    throw 'Skipped: cannot use backslash in file name'
+  endif
   enew
   %bwipe!
   e a\\b\\c

src/version.c

@@ -753,6 +753,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2098,
 /**/
     2097,
 /**/