Ensure _.merge produces dense arrays and revert accepting arrays of arguments for _.compose, _.defaults, _.extend, and _.merge.

Former-commit-id: a02772f8be04e187cbbfeb324cd4fb4318098162

build/pre-compile.js

@@ -7,13 +7,10 @@
 
   /** Used to minify variables embedded in compiled strings */
   var compiledVars = [
-    'args',
     'argsIndex',
     'argsLength',
-    'arrayRef',
     'callback',
     'collection',
-    'concat',
     'createCallback',
     'ctor',
     'guard',