add makeBinPath function for abstracting away pkg/bin:pkg2/bin..

lib/strings.nix

@@ -52,6 +52,10 @@ rec {
   # libraries for a set of packages, e.g. "${pkg1}/lib:${pkg2}/lib:...".
   makeLibraryPath = makeSearchPath "lib";
 
+  # Construct a binary search path (such as $PATH) containing the
+  # binaries for a set of packages, e.g. "${pkg1}/bin:${pkg2}/bin:...".
+  makeBinPath = makeSearchPath "bin";
+
 
   # Idem for Perl search paths.
   makePerlPath = makeSearchPath "lib/perl5/site_perl";