Added assert_var_set() - part of trying to deprecate required_variable (which

is used in two different ways)

lib/moodlelib.php

@@ -351,6 +351,19 @@ function confirm_sesskey($sesskey=NULL) {
 }
 
 
+/**
+ * Improved ensure a variable is set
+ * Issue a (custom) error message if not
+ * @param mixed $var the variable
+ * @param string $error optional additional error message
+ */
+function assert_var_set( $var, $error='' ) {
+  if (! isset($var)) {
+    error( "a required variable is not set - $error" );
+  }
+}
+
+
 /**
  * Ensure that a variable is set
  *
@@ -371,7 +384,6 @@ function require_variable($var) {
  * Ensure that a variable is set
  *
  * If $var is undefined set it (by reference), otherwise return $var.
- * This function will soon be made obsolete by {@link optional_param()}
  *
  * @param mixed $var the variable which may be unset
  * @param mixed $default the value to return if $var is unset