patch 8.1.0274: 'incsearch' triggers on ":source"

Problem:    'incsearch' triggers on ":source".
Solution:   Check for the whole command name.

src/version.c

@@ -794,6 +794,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    274,
 /**/
     273,
 /**/