Shorten the synopsis that gets into the table of contents.

Doc/lib/libimghdr.tex

 \section{\module{imghdr} ---
-         Determine the type of image contained in a file or byte stream.}
+         Determine the type of an image.}
 \declaremodule{standard}{imghdr}
 
 \modulesynopsis{Determine the type of image contained in a file or byte stream.}