Fix for sourcemap file locations

babel-loader was setting `options.sourceFileName` to a relative path,
but this does not seem to work correctly anymore with either webpack or
babel itself and causes incorrect source map file data in webpack.

Setting it to an absolute path seems to fix the problem.

Fixes babel#480 and possibly also babel#93.

package.json

@@ -74,7 +74,7 @@
   "nyc": {
     "all": true,
     "include": [
-      "src/**/*.js"
+      "lib/**/*.js"
     ],
     "reporter": [
       "text",

src/index.js

@@ -3,7 +3,6 @@ const loaderUtils = require("loader-utils");
 const path = require("path");
 const cache = require("./fs-cache.js");
 const exists = require("./utils/exists");
-const relative = require("./utils/relative");
 const read = require("./utils/read");
 const resolveRc = require("./resolve-rc.js");
 const pkg = require("../package.json");
@@ -143,7 +142,7 @@ module.exports = function(source, inputSourceMap) {
   }
 
   if (options.sourceFileName === undefined) {
-    options.sourceFileName = relative(options.sourceRoot, options.filename);
+    options.sourceFileName = options.filename;
   }
 
   const cacheDirectory = options.cacheDirectory;