Fix some bugs in UseDoxygen.cmake

There was a bug in the definition of `DOXYFILE_LATEX`, and _another_
in the processing of it (which were the only reason it wasn't
defaulting on, the way it appeared to be configured), fixed the
bug and changed it to default OFF. But now it _can_ be enabled.

Also moved the handling of `DOXYFILE_DOT` out of the latex-only
section, so that it can be turned on with the new config variable
`DOXYFILE_USE_DOT` (default on). If `DOXYFILE_USE_DOT` is enabled
and the `dot` executable is found, `DOXYFILE_DOT` will be set "YES"
and `dot` will be used for the HTML as well, giving better graphs.

cmake/Modules/UseDoxygen.cmake

@@ -105,12 +105,18 @@ if(DOXYGEN_FOUND AND DOXYFILE_IN_FOUND)
 		STRING "Additional source files/directories separated by space")
 	set(DOXYFILE_SOURE_DIRS "\"${DOXYFILE_SOURCE_DIR}\" ${DOXYFILE_EXTRA_SOURCES}")
 
-	usedoxygen_set_default(DOXYFILE_LATEX YES BOOL "Generate LaTeX API documentation" OFF)
+	usedoxygen_set_default(DOXYFILE_LATEX OFF BOOL "Generate LaTeX API documentation")
 	usedoxygen_set_default(DOXYFILE_LATEX_DIR "latex" STRING "LaTex output directory")
 
 	mark_as_advanced(DOXYFILE_OUTPUT_DIR DOXYFILE_HTML_DIR DOXYFILE_LATEX_DIR
 		DOXYFILE_SOURCE_DIR DOXYFILE_EXTRA_SOURCE_DIRS DOXYFILE_IN)
 
+	## Dot
+	usedoxygen_set_default(DOXYFILE_USE_DOT ON BOOL "Use dot (part of graphviz) to generate graphs")
+	set(DOXYFILE_DOT "NO")
+	if(DOXYFILE_USE_DOT AND DOXYGEN_DOT_EXECUTABLE)
+		set(DOXYFILE_DOT "YES")
+	endif()
 
 	set_property(DIRECTORY 
 		APPEND PROPERTY
@@ -125,13 +131,12 @@ if(DOXYGEN_FOUND AND DOXYFILE_IN_FOUND)
 
 	## LaTeX
 	set(DOXYFILE_PDFLATEX "NO")
-	set(DOXYFILE_DOT "NO")
 
 	set_property(DIRECTORY APPEND PROPERTY
 		ADDITIONAL_MAKE_CLEAN_FILES
 		"${DOXYFILE_OUTPUT_DIR}/${DOXYFILE_LATEX_DIR}")
 
-	if(DOXYFILE_LATEX STREQUAL "ON")
+	if(DOXYFILE_LATEX)
 		set(DOXYFILE_GENERATE_LATEX "YES")
 		find_package(LATEX)
 		find_program(DOXYFILE_MAKE make)
@@ -140,9 +145,6 @@ if(DOXYGEN_FOUND AND DOXYFILE_IN_FOUND)
 			if(PDFLATEX_COMPILER)
 				set(DOXYFILE_PDFLATEX "YES")
 			endif()
-			if(DOXYGEN_DOT_EXECUTABLE)
-				set(DOXYFILE_DOT "YES")
-			endif()
 
 			add_custom_command(TARGET doxygen
 				POST_BUILD