Only ignore embedded JSON/YAML/properties file extensions

Prior to this patch, setting `ignore_file_extension` had two unexpected
effects:

  1. Any path containing `.` would be truncated
  2. Paths which did not include periods would simply be removed from the
     key/value store:

     ```
     > var file = 'foo/bar/baz';
     undefined
     > file = file.substr(0, file.lastIndexOf('.'));
     ''
     ```

This patch makes `ignore_file_extensions` less greedy. `create_key_name()` will
only remove the extension when:

  1. the extension matches `.json`, `.yaml`, `.yml`, or `.properties`, and
  2. `expand_keys` is enabled.

Closes #56.

lib/consul/index.js

@@ -10,6 +10,8 @@ var consul = require('consul')({'host': global.endpoint, 'port': global.port, 's
 
 var token = undefined;
 
+const EXPAND_EXTENSIONS = ['json', 'yaml', 'yml', 'properties'];
+
 // This makes life a bit easier for expand_keys mode, allowing us to check for a .json
 // extension with less code per line.
 String.prototype.endsWith = function(suffix) {
@@ -60,9 +62,12 @@ var create_key_name = function(branch, file, ref) {
     file = file.substring(branch.source_root.length + 1);
   }
 
-  // Ignore file extensoion on demand
-  if (branch.ignore_file_extension) {
-    file = file.substr(0, file.lastIndexOf("."));
+  // Remove extension from the key name when expanding an embedded document.
+  if (branch.ignore_file_extension && (branch.expand_keys || branch.expand_keys_diff)) {
+    var extension = file.substr(file.lastIndexOf('.') + 1);
+    if (_.contains(EXPAND_EXTENSIONS, extension)) {
+      file = file.substr(0, file.lastIndexOf('.'));
+    }
   }
   key_parts.push(file);
   return key_parts.join('/');