check-headers.pl: check class comment more robustly
check-headers.pl: check class comment more robustly

It should never be the case that the class comment contains only
annotations such as "@author" without an actual comment preceding them.

biovoxxel/imagej,biovoxxel/imagej,TehSAUCE/imagej,TehSAUCE/imagej,TehSAUCE/imagej,biovoxxel/imagej