* iface/gspn/common.cc, iface/gspn/common.hh,

src/ltlast/atomic_prop.cc, src/ltlast/atomic_prop.hh,
src/ltlparse/fmterror.cc, src/ltlparse/public.hh,
src/ltlvisit/dotty.cc, src/ltlvisit/dotty.hh,
src/ltlvisit/dump.cc, src/ltlvisit/dump.hh,
src/ltlvisit/tostring.cc, src/ltlvisit/tostring.hh,
src/misc/escape.cc, src/misc/escape.hh, src/tgba/bdddict.cc,
src/tgba/bdddict.hh, src/tgba/bddprint.cc, src/tgba/bddprint.hh,
src/tgbaalgos/dotty.cc, src/tgbaalgos/dotty.hh,
src/tgbaalgos/lbtt.cc, src/tgbaalgos/lbtt.hh,
src/tgbaalgos/neverclaim.cc, src/tgbaalgos/neverclaim.hh,
src/tgbaalgos/save.cc, src/tgbaalgos/save.hh,
src/tgbaalgos/gtec/status.cc, src/tgbaalgos/gtec/status.hh,
src/tgbaparse/fmterror.cc, src/tgbaparse/public.hh: Include <iosfwd>
in headers, and prefer <ostream> in the body whenever possible.
* src/sanity/style.test, HACKING: Check and document this.

src/sanity/style.test

@@ -1,3 +1,4 @@
+
 #! /bin/sh
 
 # Ensure consistent style by catching common improper constructs.
@@ -113,9 +114,21 @@ for dir in "${INCDIR-..}" "${INCDIR-..}"/../iface; do
     grep -e 'return[	 ]*[(][^(]*[)];' $tmp &&
       diag 'No useless parentheses after return.'
 
-    grep  'NULL' $tmp &&
+    grep 'NULL' $tmp &&
       diag 'Use 0 instead of NULL.  NULL is not portable.'
 
+    case $file in
+      *.hh | *.hxx)
+        if grep -e '(cout|cerr|clog)' $tmp >/dev/null; then
+          :
+	else
+          grep '#.*include.*<iostream>' $tmp &&
+            diag 'Avoid <iostream> in headers, better use <iosfwd>.'
+        fi
+        ;;
+    esac
+
+
     $fail && echo "$file" >>failures
   done
 done