vim patches 7.4.955/974/975/989. #3919

Helped by @Shougo.

vim-patch:7.4.955
vim-patch:7.4.974
vim-patch:7.4.975
vim-patch:7.4.989

Port upstream vim patches 955, 974, 975 and 989. Mark patches
964, 968, 970, and 971, and 982 as NA. Update patch list to 1022.

patch 7.4.955
Problem:    Vim doesn't recognize .pl6 and .pod6 files.
Solution:   Recognize them as perl6 and pod6. (Mike Eve)

patch 7.4.974
Problem:    When using :diffsplit the cursor jumps to the first line.
Solution:   Put the cursor on the line related to where the cursor was before
            the split.

patch 7.4.975
Problem:    Using ":sort" on a very big file sometimes causes text to be
            corrupted. (John Beckett)
Solution:   Copy the line into a buffer before calling ml_append().

patch 7.4.989
Problem:    Leaking memory when hash_add() fails. Coverity error 99126.
Solution:   When hash_add() fails free the memory.

778 marked as not NA as it will be needed once vim patch 754 is merged

Marked as NA:
964 test 87 was deleted
968 tests 86/87 were deleted
970 guarded by: `# if defined(FEAT_GUI_GTK) || defined(PROTO`
    and is inside a function that no longer exists
971 function table already sorted correctly
982 marked as NA because Neovim tests are only specified in exactly one location

src/nvim/version.c

@@ -135,32 +135,32 @@ static int included_patches[] = {
   // 992 NA
   // 991,
   // 990 NA
-  // 989,
+  989,
   // 988 NA
   // 987 NA
   // 986 NA
   // 985 NA
   // 984,
   // 983,
-  // 982,
+  // 982 NA
   // 981,
   // 980,
   // 979 NA
   // 978,
   // 977,
   // 976 NA
-  // 975,
+  975,
   // 974,
   // 973,
-  // 972,
-  // 971,
-  // 970,
+  972,
+  // 971 NA
+  // 970 NA
   // 969,
-  // 968,
+  // 968 NA
   // 967 NA
   // 966 NA
   // 965 NA
-  // 964,
+  // 964 NA
   // 963,
   // 962 NA
   // 961,
@@ -169,7 +169,7 @@ static int included_patches[] = {
   // 958,
   // 957,
   // 956,
-  // 955,
+  955,
   // 954 NA
   953,
   // 952,
@@ -346,7 +346,7 @@ static int included_patches[] = {
   781,
   // 780 NA
   // 779,
-  // 778 NA
+  // 778,
   // 777 NA
   776,
   775,