Bug 159247 Implement toString() in class StringFormatValue, NumberFormatValue and DateTimeFormatValue
Engine need the implementation of toString() method in class StringFormatValue, NumberFormatValue and DateTimeFormatValue.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/api/elements/structures/FormatValue.java
if ( PATTERN_MEMBER.equals( memberName ) )
			return value;
		assert false;
		return null;
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.birt.report.model.core.Structure#setIntrinsicProperty(java.lang.String,
	 *      java.lang.Object)
	 */
	protected void setIntrinsicProperty( String memberName, Object value )
	{
		if ( CATEGORY_MEMBER.equals( memberName ) )
			name = (String) value;
		else if ( PATTERN_MEMBER.equals( memberName ) )
			this.value = (String) value;
		else
			assert false;
	}
	/**
	 * Returns the variable name.
	 * 
	 * @return the variable name
	 */
	public String getCategory( )
	{
		return (String) getProperty( null, CATEGORY_MEMBER );
	}
	/**