use svg in doxygen and ensure dot is around for it

debian/control

@@ -9,7 +9,7 @@ Build-Depends: dpkg-dev (>= 1.15.8), debhelper (>= 8.1.3~), libdb-dev,
  gettext (>= 0.12), libcurl4-gnutls-dev (>= 7.19.4~),
  zlib1g-dev, libbz2-dev, xsltproc, docbook-xsl, docbook-xml,
  po4a (>= 0.34-2), autotools-dev, autoconf, automake
-Build-Depends-Indep: doxygen, debiandoc-sgml
+Build-Depends-Indep: doxygen, debiandoc-sgml, graphviz
 Build-Conflicts: autoconf2.13, automake1.4
 Vcs-Git: git://anonscm.debian.org/apt/apt.git
 Vcs-Browser: http://anonscm.debian.org/gitweb/?p=apt/apt.git

doc/Doxyfile.in

@@ -880,7 +880,7 @@ HTML_OUTPUT            = html
 # each generated HTML page (for example: .htm,.php,.asp). If it is left blank
 # doxygen will generate files with .html extension.
 
-HTML_FILE_EXTENSION    = .html
+HTML_FILE_EXTENSION    = .xhtml
 
 # The HTML_HEADER tag can be used to specify a personal HTML header for
 # each generated HTML page. If it is left blank doxygen will generate a
@@ -1715,7 +1715,7 @@ DOT_NUM_THREADS        = 0
 # the DOTFONTPATH environment variable or by setting DOT_FONTPATH to the
 # directory containing the font.
 
-DOT_FONTNAME           = FreeSans
+DOT_FONTNAME           =
 
 # The DOT_FONTSIZE tag can be used to set the size of the font of dot graphs.
 # The default size is 10pt.
@@ -1815,7 +1815,7 @@ DIRECTORY_GRAPH        = YES
 # HTML_FILE_EXTENSION to xhtml in order to make the SVG files
 # visible in IE 9+ (other browsers do not have this requirement).
 
-DOT_IMAGE_FORMAT       = png
+DOT_IMAGE_FORMAT       = svg
 
 # If DOT_IMAGE_FORMAT is set to svg, then this option can be set to YES to
 # enable generation of interactive SVG images that allow zooming and panning.
@@ -1824,7 +1824,7 @@ DOT_IMAGE_FORMAT       = png
 # need to set HTML_FILE_EXTENSION to xhtml in order to make the SVG files
 # visible. Older versions of IE do not have SVG support.
 
-INTERACTIVE_SVG        = NO
+INTERACTIVE_SVG        = YES
 
 # The tag DOT_PATH can be used to specify the path where the dot tool can be
 # found. If left blank, it is assumed the dot tool can be found in the path.