Fix for #198.

GCC-4.2.1 is unable to compile code like this:

    std::vector<int> v;
    std::vector<int>::const_reverse_iterator i;
    for (i = v.rbegin(); i != v.rend(); ++i) ;

It's unable to deduce const overload for 'rend':

    "no match for ‘operator!=’ in ‘i != std::vector<_Tp, _Alloc>::rend()"

However, the following code compiles fine:

    std::vector<int> v;
    std::vector<int>::const_reverse_iterator i = v.rbegin(), e = v.rend();
    for (i != e; ++i) ;

This was reported by Ryan Shmidt.

re2c/src/code/bitmap.cc

@@ -27,7 +27,8 @@ bitmaps_t::~bitmaps_t()
 
 void bitmaps_t::insert(const Go *go, const State *s)
 {
-	for (rciter_t i = maps.rbegin(); i != maps.rend(); ++i) {
+	rciter_t i = maps.rbegin(), e = maps.rend();
+	for (; i != e; ++i) {
 		if (matches(i->go, i->on, go, s)) return;
 	}
 
@@ -37,7 +38,8 @@ void bitmaps_t::insert(const Go *go, const State *s)
 
 const bitmap_t *bitmaps_t::find(const Go *go, const State *s) const
 {
-	for (rciter_t i = maps.rbegin(); i != maps.rend(); ++i) {
+	rciter_t i = maps.rbegin(), e = maps.rend();
+	for (; i != e; ++i) {
 		if (i->on == s && matches(i->go, i->on, go, s)) return &(*i);
 	}
 	return NULL;