So I decided to clean them up. For your pleasure, here's a little script that does it. Save it as mp-clean somewhere on your system, and run as:

• mp-clean test: This will scan your entire disk and report how many savefiles it finds, and their total size. It may run for a looooong time, so don't be impatient!

  A save-file is a file that ends in .mp followed by a number, and there must be a corresponding "real" file in the same directory. E.g., a save-file /opt/local/include/hdr.h.mp_123456 is only a save-file if the corresponding file /opt/local/include/hdr.h exists.

• mp-clean test /opt/local/include: This is like the above, except that only /opt/local/include and its subdirectories are scanned.
• mp-clean go and mp-clean go /opt/local/include don't only locate the files and report their total size, but they also remove them. This is the actual cleaner.

Finally, here's the little script.

#!/usr/bin/perl

use strict;
$|++;

# Command line
my $action   = shift(@ARGV);
my $startdir = shift(@ARGV);
$startdir = '/' if ($startdir eq '');
die ("Usage: mp-clean test|go [startdir]\n",
     "Cleans up mp-savefiles from port. Default startdir is /\n")
  if ($#ARGV != -1 or ($action ne 'go' and $action ne 'test'));

# Locate the mp files.
open (my $if, "find $startdir -name '*.mp_*' |")
  or die ("Cannot start find\n");
my $totfiles = 0;
my $mpfiles = 0;
my $bytescleaned = 0;
while (my $mpfile = <$if>) {
    $totfiles++;
    chomp ($mpfile);
    print ("$totfiles files seen (at $mpfile)\n");
    
    my $orgfile = $mpfile;
    $orgfile =~ s{\.mp_[0-9]+$}{};
    next unless (-f $orgfile);
    $mpfiles++;
    
    $bytescleaned += (stat($mpfile))[7];

    if ($action eq 'go') {
        unlink ($mpfile) or die ("\nCannot unlink '$mpfile': $!\n");
    }
}

print ("\n",
       "Found MP files:        $mpfiles\n",
       "Total size MP files:   $bytescleaned\n");