patch 8.2.2468: not easy to get the full command name from a shortened one

Problem:    Not easy to get the full command name from a shortened one.
Solution:   Add fullcommand(). (Martin Tournoij, closes #7777)
diff --git a/src/proto/evalfunc.pro b/src/proto/evalfunc.pro
index 13dffac..2b19448 100644
--- a/src/proto/evalfunc.pro
+++ b/src/proto/evalfunc.pro
@@ -23,4 +23,5 @@
 float_T vim_round(float_T f);
 long do_searchpair(char_u *spat, char_u *mpat, char_u *epat, int dir, typval_T *skip, int flags, pos_T *match_pos, linenr_T lnum_stop, long time_limit);
 void f_string(typval_T *argvars, typval_T *rettv);
+void f_fullcommand(typval_T *argvars, typval_T *rettv);
 /* vim: set ft=c : */