default new constructors assume strings are mnemonics instead of labels where applicable

[Ross McFarland <rwmcfa1 neces com>]

things like GtkButton that used to have the following behavior:

$btn = Gtk2::Button->new('label string');

now have the following:

$btn = Gtk2::Button->new('mnemonic label string');

in sentence form:

the default behavior for new when a string is passed on such widgets is
now to use the string as a mnemonic instead of a label. the label
version is still accessible as ->new_with_label. ->new_with_mnemonic
still works as well. 

take a look at ChangeLog to see what was affected.

-rm