Have cmake set doxygen to use dot if it's available.

Also a minor typos

src/Doc/BuildDevDoc.cfg.in

@@ -1566,7 +1566,7 @@ HIDE_UNDOC_RELATIONS   = YES
 # toolkit from AT&T and Lucent Bell Labs. The other options in this section
 # have no effect if this option is set to NO (the default)
 
-HAVE_DOT               = NO
+HAVE_DOT               = @HAVE_DOT@
 
 # The DOT_NUM_THREADS specifies the number of dot invocations doxygen is
 # allowed to run in parallel. When set to 0 (the default) doxygen will

src/Doc/CMakeLists.txt

@@ -4,6 +4,7 @@ if(DOXYGEN_FOUND)
     IF (DOXYGEN_DOT_EXECUTABLE)
         SET(HAVE_DOT YES)
     ELSE (DOXYGEN_DOT_EXECUTABLE)
+        message("Note: Doxygen docs will look better with graphviz's dot installed.")
         SET(HAVE_DOT NO)
     ENDIF (DOXYGEN_DOT_EXECUTABLE)
 

src/Doc/doctips.dox

@@ -1,6 +1,9 @@
 /** \page doctips Documenting FreeCAD's code
 
-Below are a few remarks and notes about Doxygen usage for FreeCAD, gathered after examining and removing most of the warnings emited by Doxygen:
+Below are a few remarks and notes about Doxygen usage for FreeCAD,
+gathered after examining and removing most of the warnings emitted
+by Doxygen.  For information on (re)building the source docs, see
+\ref makingdocs
 
 - Pay attention to warnings emited by doxygen when building the doc.
   The item giving rise to the warning will be skipped and will not be

src/Doc/mainpage.dox

@@ -38,7 +38,7 @@
   <a href="http://www.freecadweb.org/wiki/index.php?title=Main_Page">Wiki</a>
 
   FreeCAD being a fast moving target, don't hesitate to rebuild an up to
-  date doc from svn source as often as needed. CPU cycles are cheap
+  date doc from source as often as needed (\ref makingdocs "more info"). CPU cycles are cheap
   nowadays! 
 
   The homepage of FreeCAD is <a href="http://www.freecadweb.org">here</a>.