This works as well...

#!/usr/bin/perl -w
use strict;

my $last_line;
my $i;
my $num_lines;

open(FILE, "<test.txt") || die "Unable to open file: $!";
chomp(my @lines = <FILE>);  # get the lines
close(FILE);

$num_lines = @lines;

  for($i=0; $i < $num_lines; $i++) {

    if($i == $num_lines-1) {  # make sure we don't access 
                              # uninitialized index of array
      print "$lines[$i]\n";   # print the last line
    }
    elsif($lines[$i+1] =~ m/\+/) {   # look ahead
      $lines[$i+1] =~ s/^\+//;
      print "$lines[$i] $lines[++$i]\n";
    }
    else{
      print "$lines[$i]\n";
    }
  }
[download]

Hope this helps. -Eric