Build doxygen pictures with libgd to reduce their size.
Doxygen only knows how to call dot with -Tpng, while using -Tpng:gd produces pictures that are 10 times smaller. Use a simple wrapper around dot to simplify this. * doc/dot.in: New file, that wrap the system's dot and replace -Tpng by -Tpng:gd. * doc/Makefile.am ($(srcdir)/stamp): Depend on dot. * doc/Doxyfile.in: Update to 1.6.2. (DOT_PATH): Set to @srcdir@ to use doc/dot instead of the system's dot. * configure.ac: Find the absolute path of dot, and generate the doc/dot script.