Added a minimal runtime library.

The runtime library can be compiled using './build-runtime'.
Added an internal framework to write the code of native methods.
Extended the runtime library regarding subclasses of java.lang.Number.
Implemented a draft version of Object.toString().
Added java.lang Throwables in the runtime library.
Many unrelated changes, that are the result of a long test-driven debuggin session.
Fixed bugs related to new method hash algorithm.
Added a distinction in String.oz between toRawString() et toRawVS().
Added support for arrays.
Fixed: primitive class constants.
Added proper initialization of fields (and array items).

According to the Scala specification, all fields must be initialized to their 'zero'.
Added boxing and unboxing of all primitive types.
Fixed scala.runtime.IntRef and added scala.runtime.BooleanRef in the runtime library.
Added support for try..catch..finally statements.
Fixed isInstanceOf and asInstanceOf regarding null values.
Implemented the method String.equals().
Added support for the == operator on references (uses the equals() method.
Added MatchError.scala in the runtime library.
Added support for 'return' statements (both local and non-local).
Added support for a true --classpath command-line parameter.

So now we do not need the symlinks to runtime/java/ and runtime/scala/ anymore.