Use portable shebangs instead of hardcoding interpreters
See also: https://blogs.gentoo.org/mgorny/2016/02/08/a-quick-note-on-portable-shebangs/

--- a/scripts/dnadiff.pl
+++ b/scripts/dnadiff.pl
@@ -1,4 +1,4 @@
-#!__PERL_PATH -w
+#!/usr/bin/env perl
 
 #-------------------------------------------------------------------------------
 #   Programmer: Adam M Phillippy, University of Maryland
--- a/scripts/exact-tandems.csh
+++ b/scripts/exact-tandems.csh
@@ -1,4 +1,4 @@
-#!__CSH_PATH -f
+#!/usr/bin/env csh
 #
 # Find exact tandem repeats in specified file involving an
 # exact duplicate of at least the specified length
--- a/scripts/mapview.pl
+++ b/scripts/mapview.pl
@@ -1,4 +1,4 @@
-#!__PERL_PATH
+#!/usr/bin/env perl
 
 use lib "__SCRIPT_DIR";
 use Foundation;
--- a/scripts/mummerplot.pl
+++ b/scripts/mummerplot.pl
@@ -1,4 +1,4 @@
-#!__PERL_PATH
+#!/usr/bin/env perl
 
 ################################################################################
 #   Programmer: Adam M Phillippy, The Institute for Genomic Research
--- a/scripts/nucmer2xfig.pl
+++ b/scripts/nucmer2xfig.pl
@@ -1,4 +1,4 @@
-#!__PERL_PATH
+#!/usr/bin/env perl
 # (c) Steven Salzberg 2001
 # Make an xfig plot for a comparison of a reference chromosome (or single
 # molecule) versus a multifasta file of contigs from another genome.  
--- a/scripts/nucmer.pl
+++ b/scripts/nucmer.pl
@@ -1,4 +1,4 @@
-#!__PERL_PATH
+#!/usr/bin/env perl
 
 #-------------------------------------------------------------------------------
 #   Programmer: Adam M Phillippy, The Institute for Genomic Research
--- a/scripts/promer.pl
+++ b/scripts/promer.pl
@@ -1,4 +1,4 @@
-#!__PERL_PATH
+#!/usr/bin/env perl
 
 #-------------------------------------------------------------------------------
 #   Programmer: Adam M Phillippy, The Institute for Genomic Research
--- a/scripts/run-mummer1.csh
+++ b/scripts/run-mummer1.csh
@@ -1,4 +1,4 @@
-#!__CSH_PATH -f
+#!/usr/bin/env csh
 #
 # **SEVERELY** antiquated script for running the mummer 1 suite
 # -r option reverse complements the query sequence, coordinates of the reverse
--- a/scripts/run-mummer3.csh
+++ b/scripts/run-mummer3.csh
@@ -1,4 +1,4 @@
-#!__CSH_PATH -f
+#!/usr/bin/env csh
 #
 # for running the basic mummer 3 suite, should use nucmer instead when possible
 # to avoid the confusing reverse coordinate system of the raw programs.