patch 8.1.0105: all tab stops are the same

Problem:    All tab stops are the same.
Solution:   Add the variable tabstop feature. (Christian Brabandt,
            closes #2711)
diff --git a/src/proto/misc1.pro b/src/proto/misc1.pro
index 0e1d22e..58c3d3f 100644
--- a/src/proto/misc1.pro
+++ b/src/proto/misc1.pro
@@ -3,6 +3,7 @@
 int get_indent_lnum(linenr_T lnum);
 int get_indent_buf(buf_T *buf, linenr_T lnum);
 int get_indent_str(char_u *ptr, int ts, int list);
+int get_indent_str_vtab(char_u *ptr, int ts, int *vts, int list);
 int set_indent(int size, int flags);
 int get_number_indent(linenr_T lnum);
 int get_breakindent_win(win_T *wp, char_u *line);