vim-patch:8.2.1961: various comments can be improved

Problem:    Various comments can be improved.
Solution:   Various comment adjustments.
22286895fc

src/nvim/eval/typval.c

@@ -1358,7 +1358,8 @@ void tv_dict_item_remove(dict_T *const dict, dictitem_T *const item)
 
 //{{{2 Alloc/free
 
-/// Allocate an empty dictionary
+/// Allocate an empty dictionary.
+/// Caller should take care of the reference count.
 ///
 /// @return [allocated] new dictionary.
 dict_T *tv_dict_alloc(void)

src/nvim/eval/typval.h

@@ -301,7 +301,8 @@ struct funccall_S {
   int dbg_tick;  ///< Debug_tick when breakpoint was set.
   int level;  ///< Top nesting level of executed function.
   proftime_T prof_child;  ///< Time spent in a child.
-  funccall_T *caller;  ///< Calling function or NULL.
+  funccall_T *caller;  ///< Calling function or NULL; or next funccal in
+                       ///< list pointed to by previous_funccal.
   int fc_refcount;  ///< Number of user functions that reference this funccall.
   int fc_copyID;  ///< CopyID used for garbage collection.
   garray_T fc_funcs;  ///< List of ufunc_T* which keep a reference to "func".

src/nvim/testdir/shared.vim

@@ -243,7 +243,7 @@ func s:feedkeys(timer)
   call feedkeys('x', 'nt')
 endfunc
 
-" Get $VIMPROG to run Vim executable.
+" Get $VIMPROG to run the Vim executable.
 " The Makefile writes it as the first line in the "vimcmd" file.
 " Nvim: uses $NVIM_TEST_ARG0.
 func GetVimProg()