Fix external relative paths on Windows

Replace backslashes with forward slashes when adding relative paths for
external references.

index.js

@@ -30,7 +30,8 @@ inherits(Browserify, EventEmitter);
 
 var fs = require('fs');
 var path = require('path');
-var relativePath = require('cached-path-relative')
+var cachedPathRelative = require('cached-path-relative');
+
 var paths = {
     empty: path.join(__dirname, 'lib/_empty.js')
 };
@@ -136,14 +137,12 @@ Browserify.prototype.require = function (file, opts) {
     var expose = opts.expose;
     if (file === expose && /^[\.]/.test(expose)) {
         expose = '/' + relativePath(basedir, expose);
-        expose = expose.replace(/\\/g, '/');
     }
     if (expose === undefined && this._options.exposeAll) {
         expose = true;
     }
     if (expose === true) {
         expose = '/' + relativePath(basedir, file);
-        expose = expose.replace(/\\/g, '/');
     }
 
     if (isStream(file)) {
@@ -789,8 +788,7 @@ Browserify.prototype._debug = function (opts) {
     return through.obj(function (row, enc, next) {
         if (opts.debug) {
             row.sourceRoot = 'file://localhost';
-            row.sourceFile = relativePath(basedir, row.file)
-                .replace(/\\/g, '/');
+            row.sourceFile = relativePath(basedir, row.file);
         }
         this.push(row);
         next();
@@ -855,3 +853,7 @@ function isExternalModule (file) {
         /^[\/.]/;
     return !regexp.test(file);
 }
+function relativePath (from, to) {
+    // Replace \ with / for OS-independent behavior
+    return cachedPathRelative(from, to).replace(/\\/g, '/');
+}