patch 8.2.0869: it is not possible to customize the quickfix window contents

Problem:    It is not possible to customize the quickfix window contents.
Solution:   Add 'quickfixtextfunc'. (Yegappan Lakshmanan, closes #5465)
diff --git a/src/option.h b/src/option.h
index bead4c5..718553a 100644
--- a/src/option.h
+++ b/src/option.h
@@ -820,6 +820,7 @@
 EXTERN char_u	*p_ruf;		// 'rulerformat'
 #endif
 EXTERN char_u	*p_pp;		// 'packpath'
+EXTERN char_u	*p_qftf;	// 'quickfixtextfunc'
 EXTERN char_u	*p_rtp;		// 'runtimepath'
 EXTERN long	p_sj;		// 'scrolljump'
 #if defined(MSWIN) && defined(FEAT_GUI)