add new trigger to prevent certain naming clashes

BitKeeper/triggers/pre-commit.check-case.pl:
  catch duplicate file names, ignoring capitalisation, mostly to avoid changesets where a deleted file foobar and a deleted file FooBar break a tree on case insensitive file systems

BitKeeper/triggers/pre-commit.check-case.pl

+#!/usr/bin/perl
+my $status = 0;
+
+my $pending = $ENV{'BK_PENDING'};
+exit 0 unless -f $pending;
+
+open FI, "<", $pending || exit 0;
+while(<FI>) {
+	my ($file, $stuff) = split /\|/, $_, 2;
+	next unless -f $file;
+	$file =~ s/^(.*)\/([^\/]*)$/$2/;
+	my $path = $1;
+	opendir DIR, $path;
+	my @files = sort map { lc } readdir DIR;
+	closedir DIR;
+	my %count = ();
+	$count{$_}++ for @files;
+	@files = grep { $count{$_} > 1 } keys %count;
+	if(@files > 0) {
+		print "$path/$file: duplicate file names: " . (join " ", @files) . "\n";
+		$status = 1;
+	}
+}
+close FI;
+
+exit $status;