Add preventIndent option for partials

This disables the standalone partial indent behavior required by the Mustache spec and allows for users to utilize partials in the same manner as under 1.x.

Fixes #858

spec/env/common.js

@@ -18,7 +18,7 @@ global.compileWithPartials = function(string, hashOrArray, partials) {
     ary = [];
     ary.push(hashOrArray[0]);
     ary.push({ helpers: hashOrArray[1], partials: hashOrArray[2] });
-    options = {compat: hashOrArray[3]};
+    options = typeof hashOrArray[3] === 'object' ? hashOrArray[3] : {compat: hashOrArray[3]};
     if (hashOrArray[4] != null) {
       options.data = !!hashOrArray[4];
       ary[1].data = hashOrArray[4];