Patch to improve style of generate_history.pl perl script

diff --git a/doc/src/sgml/generate_history.pl b/doc/src/sgml/generate_history.pl
new file mode 100644
index 2b81569..a6c0bd7
*** a/doc/src/sgml/generate_history.pl
--- b/doc/src/sgml/generate_history.pl
***************
*** 13,22 ****
  
  use strict;
  
! my($srcdir) = shift;
! defined($srcdir) || die "$0: missing required argument: srcdir\n";
! my($infile) = shift;
! defined($infile) || die "$0: missing required argument: inputfile\n";
  
  # Emit DOCTYPE header so that the output is a self-contained SGML document
  print "<!DOCTYPE appendix PUBLIC \"-//OASIS//DTD DocBook V4.2//EN\">\n";
--- 13,22 ----
  
  use strict;
  
! my $srcdir = shift;
! die "$0: missing required argument: srcdir\n" if !defined($srcdir);
! my $infile = shift;
! die "$0: missing required argument: inputfile\n" if !defined($infile);
  
  # Emit DOCTYPE header so that the output is a self-contained SGML document
  print "<!DOCTYPE appendix PUBLIC \"-//OASIS//DTD DocBook V4.2//EN\">\n";
*************** process_file($infile);
*** 26,36 ****
  exit 0;
  
  sub process_file {
!     my($filename) = @_;
  
      local *FILE;		# need a local filehandle so we can recurse
  
!     my($f) = $srcdir . '/' . $filename;
      open(FILE, $f) || die "could not read $f: $!\n";
  
      while (<FILE>) {
--- 26,36 ----
  exit 0;
  
  sub process_file {
!     my $filename = shift;
  
      local *FILE;		# need a local filehandle so we can recurse
  
!     my $f = $srcdir . '/' . $filename;
      open(FILE, $f) || die "could not read $f: $!\n";
  
      while (<FILE>) {