[perl #45013] Configure fails if prefix ends with '/'

[James Keenan via RT]

Better (to make sure that $ep is defined before we try a substitution on
it):

Index: config/init/install.pm
===================================================================
--- config/init/install.pm      (revision 21171)
+++ config/init/install.pm      (working copy)
@@ -66,7 +66,9 @@
     my ( $self, $conf ) = @_;
 
     my $prefix  = $conf->options->get('prefix')      || "/usr/local";
+    $prefix =~ s{/$}{};
     my $ep = $conf->options->get('exec-prefix');
+    $ep =~ s{/$}{} if defined $ep;
     my $eprefix = $ep ? $ep : $prefix;
 
     #  --bindir=DIR           user executables [EPREFIX/bin]