added "while_option", which needs no well-foundedness; defined "while" in terms of "while_option"
added "while_option", which needs no well-foundedness; defined "while" in terms of "while_option"

MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle