Fix for #1 - incorrect context for partials.

Partials now receive a flattened version of the parent context, including a cloned Mustache instance (if the root context is a Mustache instance). There may be issues with cloning, for example: if a pragma is enabled in the parent template, partials might also inherit the pragma.
Added (basic) test case for partials.

Mustache.php

@@ -424,7 +424,7 @@ class Mustache {
 	 * @return string
 	 */
 	protected function _renderPartial($tag_name, &$context) {
-		$view = new self($this->_getPartial($tag_name), $context, $this->_partials);
+		$view = new self($this->_getPartial($tag_name), $this->_flattenContext($context), $this->_partials);
 		$view->_otag = $this->_otag;
 		$view->_ctag = $this->_ctag;
 		return $view->render();
@@ -458,8 +458,8 @@ class Mustache {
 	 *
 	 * @access protected
 	 * @param array $context
-	 * @param mixed $local_context
-	 * @return void
+	 * @param array $local_context
+	 * @return array
 	 */
 	protected function _getContext(&$context, &$local_context) {
 		$ret = array();
@@ -470,6 +470,45 @@ class Mustache {
 		return $ret;
 	}
 
+
+	/**
+	 * Prepare a new (flattened) context.
+	 *
+	 * This is used to create a view object or array for rendering partials.
+	 *
+	 * @access protected
+	 * @param array &$context
+	 * @return array
+	 * @throws MustacheException
+	 */
+	protected function _flattenContext(&$context) {
+		$keys = array_keys($context);
+		$first = $context[$keys[0]];
+
+		if ($first instanceof Mustache) {
+			$ret = clone $first;
+			unset($keys[0]);
+
+			foreach ($keys as $name) {
+				foreach ($context[$name] as $key => $val) {
+					$ret->$key =& $val;
+				}
+			}
+		} else if (is_array($first)) {
+			$ret = array();
+
+			foreach ($keys as $name) {
+				foreach ($context[$name] as $key => $val) {
+					$ret[$key] =& $val;
+				}
+			}
+		} else {
+			throw new MustacheException('Unknown root context type.');
+		}
+
+		return $ret;
+	}
+
 	/**
 	 * Get a variable from the context array.
 	 *