examples: fix annoying off-by-one errors

* examples/extexi: Since we issue #lines only at the beginning of
@example, leave empty line when removing content (such as @comment
lines), otherwise the lines that follow have incorrect source line
location.  This leaves ugly empty lines, but they are removed when you
tidy the output for the end user: sequences of \n are mapped to at
most two sucessive \n.

examples/extexi

@@ -60,7 +60,11 @@ sub normalize($)
 {
   local ($_) = @_;
 
-  s/^\@(c |comment|dots|end (ignore|group)|ignore|group).*\n//mg;
+  # If we just remove this lines, then the compiler's tracking of
+  # #lines is broken.  Leave lines that that accepted by all our tools
+  # (including flex, hence the leading space), and that will be easy
+  # to remove (see the Make examples-unline recipe).
+  s{^\@(c |comment|dots|end (ignore|group)|ignore|group).*}{ /**/}mg;
   s/\@value\{VERSION\}/$ENV{VERSION}/g;
   s/^\@(error|result)\{\}//mg;
   s/\@([{}@])/$1/g;

examples/local.mk

@@ -59,12 +59,8 @@ EXTRA_DIST += %D%/extracted.stamp
 dist-hook: examples-unline
 .PHONY: examples-unline
 examples-unline:
-	for e in $(extracted);			\
-	do					\
-	  e=$(distdir)/$$e;			\
-	  sed -e '/#line/d' $$e >$$e.tmp;	\
-	  mv -f $$e.tmp $$e;			\
-	done
+	cd $(distdir) && \
+	  perl -pi -0777 -e 's/#line.*\n//g;s{^ /\*\*/\n}{}mg' $(extracted)
 
 
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