Enable -Wconversion: normal.c.

Refactor summary:
- extern int opcount --> extern long opcount
- bool find_decl(..., int len, ...) --> bool find_decl(..., size_t len, ...)
  * int find_ident_under_cursor(...) --> size_t find_ident_under_cursor(...)
    - int find_ident_at_pos(...) --> size_t find_ident_at_pos(...)
    - int modify_fname(..., int *usedlen, ..., int *fnamelen) --> int modify_fname(..., size_t *usedlen, ..., size_t *fnamelen)
      * char_u *eval_vars(..., int *usedlen, ...) --> char_u *eval_vars(..., size_t *usedlen, ...)
        - int find_cmdline_var(..., int *usedlen) --> ssize_t find_cmdline_var(..., size_t *usedlen)
        - static char_u *repl_cmdline(..., int srclen, ...) --> static char_u *repl_cmdline(..., size_t srclen, ...)
    - bool get_visual_text(..., int *lenp) --> bool get_visual_text(..., size_t *lenp)
      * char_u *find_file_name_in_path(..., int len, ...) --> char_u *find_file_name_in_path(..., size_t len, ...)
        - static char_u *eval_includeexpr(..., int len) --> static char_u *eval_includeexpr(..., size_t len)
        - char_u *find_file_in_path(..., int len, ...) --> char_u *find_file_in_path(..., size_t len, ...)
          * char_u *find_file_in_path_option(..., int len, ...) --> char_u *find_file_in_path_option(..., size_t len, ...)
            - char_u *find_directory_in_path(..., int len, ...) --> char_u *find_directory_in_path(..., size_t len, ...)
      * int spell_move_to(...) --> size_t spell_move_to(...)
        - int spell_check(...) --> size_t spell_check(...)
        - static int spell_bad_len --> static size_t spell_bad_len
    - void find_pattern_in_path(..., int len, ...) --> void find_pattern_in_path(..., size_t len, ...)

Helped-by: Justin M. Keyes <justinkz@gmail.com>

src/nvim/if_cscope.c

@@ -455,18 +455,16 @@ cs_add_common (
   char        *fname2 = NULL;
   char        *ppath = NULL;
   int i;
-  int len;
-  int usedlen = 0;
+  size_t usedlen = 0;
   char_u      *fbuf = NULL;
 
   /* get the filename (arg1), expand it, and try to stat it */
   fname = xmalloc(MAXPATHL + 1);
 
   expand_env((char_u *)arg1, (char_u *)fname, MAXPATHL);
-  len = (int)STRLEN(fname);
+  size_t len = STRLEN(fname);
   fbuf = (char_u *)fname;
-  (void)modify_fname((char_u *)":p", &usedlen,
-      (char_u **)&fname, &fbuf, &len);
+  (void)modify_fname((char_u *)":p", &usedlen, (char_u **)&fname, &fbuf, &len);
   if (fname == NULL)
     goto add_err;
   fname = (char *)vim_strnsave((char_u *)fname, len);