Listed herein are language incompatibilites between 3.3 and 3.5,
that you should pay attention to when updating.

- Heartbeats were called only when players are logged on. They are now
  called regardless of logged-on players.
  However, the mudlib can activate/deactivate the calls to heartbeats
  globally by using configure_driver()

- Long exections can be detected and traced by setting DC_LONG_EXEC_TIME with
  configure_driver(). If an execution exceeds this time, the current LPC stack
  will be dumped into the debug log (execution will continue).

- Some more efuns cause a privilege violation:
  * shutdown() (bug #178)
  * garbage_collection() (bug #178)

- The special driver actions ('status', 'malloc', dumpallobj' and 'opcdump')
  were removed. They can be implemented as normal actions. Example implementations
  are provided in /mudlib/deprecated/set_is_wizard.c (#596).

- Lvalue references
  Many restrictions for lvalue refrences (&var, &(arr[i]), &(arr[i1..i2]))
  were lifted:
   * They are not limited to the original variable's scope. Therefore they
     can be returned from a function or passed to a call_out.
   * For this reason the error message "Can't trace reference assignments."
     doesn't exist anymore.
   * A range can be indexed again, so it can be used as an array replacement.
   * Multiple char references to the same string are allowed.

  Lvalue references are automatically dereferenced when they are not used as
  the left hand side of an expression without the '&' operator.

  Variables that contain an lvalue reference can be 'reseated', i.e. change
  their value without changing the lvalue they reference:
    &var = new_value_or_reference;

- Order of execution on indices
  The order of execution of sub-expressions has changed:

  Prior to 3.5:
     Array#4[Expr#3][Expr#2] = Expr#1;
  Now in 3.5:
     Array#2[Expr#3][Expr#4] = Expr#1;

  Assignments are done from right to left as usual, but the assigned-to
  expression is now evaluated left to right. (For expressions that are
  not the destination of an assignment the order of an index expression
  was before and still is left-to-right.)
