patch 9.1.0558: filetype: prolog detection can be improved

Problem:  filetype: prolog detection can be improved
Solution: Improved the Prolog file detection regex and added tests for
          all cases. (igna_martinoli)

fixes: #10835
closes: #15206

Signed-off-by: igna_martinoli <ignamartinoli@protonmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/version.c b/src/version.c
index 9c076f8..aaef85f 100644
--- a/src/version.c
+++ b/src/version.c
@@ -705,6 +705,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    558,
+/**/
     557,
 /**/
     556,