[configure] add detection of dos2unix tool

configure.in

@@ -949,6 +949,9 @@ configure_library([LABLGTK],
 
 configure_tool([DOT],[dot],[dot not found: you should install GraphViz],no)
 
+configure_tool([UNIX2DOS],[unix2dos],
+               [unix2dos not found: you should install tofrodos],no)
+
 ########################
 # Plug-in dependencies #
 ########################

share/Makefile.config.in

@@ -138,6 +138,9 @@ HAS_DOT		?=@HAS_DOT@
 
 HEADACHE 	?= headache -c $(FRAMAC_SRC)/headers/headache_config.txt
 
+UNIX2DOS        ?= @UNIX2DOS@
+HAS_UNIX2DOS    ?= @HAS_UNIX2DOS@
+
 ###########################
 # Miscellaneous variables #
 ###########################