show actual message if have_message assertion fails; fix crash when expected message is regexp
show actual message if have_message assertion fails; fix crash when expected message is regexp

asciidoctor/asciidoctor-pdf,dsisnero/asciidoctor-pdf,asciidoctor/asciidoctor-pdf,dsisnero/asciidoctor-pdf,Hextremist/asciidoctor-pdf,mojavelinux/asciidoctor-pdf,Hextremist/asciidoctor-pdf,mojavelinux/asciidoctor-pdf