Workaround broken gtkdoc-scan

doc/reference/Makefile.am

@@ -47,7 +47,11 @@ CFILE_GLOB=
 
 # Header files to ignore when scanning.
 # e.g. IGNORE_HFILES=gtkdebug.h gtkintl.h
-IGNORE_HFILES=terraserver.h terraservermapsource.h
+# Note the 'non' terraserver files currently contain non UTF8 '(C)' characters
+#  which breaks gtkdoc-scan, so work around it
+IGNORE_HFILES=terraserver.h terraservermapsource.h coords.h jpeg-marker.h jpeg-data.h
+# To find such files something like this (NB isutf8 is in the Debian moreutils package)
+# find . -name '*.[ch]' -exec isutf8 \{\} \;
 
 # Images to copy into HTML directory.
 # e.g. HTML_IMAGES=$(top_srcdir)/gtk/stock-icons/stock_about_24.png