patch 8.0.1394: cannot intercept a yank command

Problem:    Cannot intercept a yank command.
Solution:   Add the TextYankPost autocommand event. (Philippe Vaucher et al.,
            closes #2333)
diff --git a/src/fileio.c b/src/fileio.c
index fb49f28..ba9ec9e 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -6478,6 +6478,7 @@
 /*
  * Like fgets(), but if the file line is too long, it is truncated and the
  * rest of the line is thrown away.  Returns TRUE for end-of-file.
+ * If the line is truncated then buf[size - 2] will not be NUL.
  */
     int
 vim_fgets(char_u *buf, int size, FILE *fp)
@@ -7856,6 +7857,7 @@
     {"WinEnter",	EVENT_WINENTER},
     {"WinLeave",	EVENT_WINLEAVE},
     {"VimResized",	EVENT_VIMRESIZED},
+    {"TextYankPost",	EVENT_TEXTYANKPOST},
     {NULL,		(event_T)0}
 };
 
@@ -9400,6 +9402,15 @@
 }
 
 /*
+ * Return TRUE when there is a TextYankPost autocommand defined.
+ */
+    int
+has_textyankpost(void)
+{
+    return (first_autopat[(int)EVENT_TEXTYANKPOST] != NULL);
+}
+
+/*
  * Execute autocommands for "event" and file name "fname".
  * Return TRUE if some commands were executed.
  */