Improve some 'do not edit this file' comments

doc/ref/intrfc.xml

@@ -1,5 +1,3 @@
-<!-- % This file was created automatically from intrfc.msk. -->
-<!-- % DO NOT EDIT! -->
 <!-- %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -->
 <!-- %% -->
 <!-- %W intrfc.xml GAP manual Alexander Hulpke -->

doc/versiondata

@@ -1,5 +1,9 @@
-<!-- This file has been generated by the GAP build system,
- do not edit manually. -->
+<!--
+This file has been generated by the GAP build system, do not edit manually.
+Instead edit either the template file `doc/versiondata.in`, or edit
+`Makefile.rules` (which has code for generating this file), or edit
+`configure.ac` (where the value being substituted come from)
+-->
 <!ENTITY VERSIONNUMBER "4.12dev">
 <!ENTITY RELEASEDAY "today">
 <!ENTITY RELEASEYEAR "this year">

doc/versiondata.in

@@ -1,5 +1,9 @@
-<!-- This file has been generated by the GAP build system,
- do not edit manually. -->
+<!--
+This file has been generated by the GAP build system, do not edit manually.
+Instead edit either the template file `doc/versiondata.in`, or edit
+`Makefile.rules` (which has code for generating this file), or edit
+`configure.ac` (where the value being substituted come from)
+-->
 <!ENTITY VERSIONNUMBER "@PACKAGE_VERSION@">
 <!ENTITY RELEASEDAY "@GAP_RELEASEDAY@">
 <!ENTITY RELEASEYEAR "@GAP_RELEASEYEAR@">

etc/ffgen.c

@@ -56,7 +56,8 @@ unsigned int needed_bits(unsigned int x)
 void emit_code(FILE * dest, int header)
 {
  unsigned i, j;
- fprintf(dest, "/* This file is generated by etc/ffgen.c during build do not edit */\n");
+ fprintf(dest, "/* This file has been generated by etc/ffgen.c during build,\n");
+ fprintf(dest, " do not edit */\n");
  if (header) {
  fprintf(dest, "#ifndef GAP_FFDATA_H\n");
  fprintf(dest, "#define GAP_FFDATA_H\n");