Minor fixes to improve regex debugging code.

When REG_DEBUG is defined, ensure that an un-filled "struct cnfa"
is all-zeroes, not just that it has nstates == 0.  This is mainly
so that looking at "struct subre" structs in gdb doesn't distract
one with a lot of garbage fields during regex compilation.

Adjust some places that print debug output to have suitable fflush
calls afterwards.

In passing, correct an erroneous ancient comment: the concatenation
subre-s created by parsebranch() have op == '.' not ','.

Noted while fooling around with some regex performance improvements.

src/include/regex/regguts.h

@@ -368,7 +368,15 @@ struct cnfa
 	struct carc *arcs;			/* the area for the lists */
 };
 
+/*
+ * When debugging, it's helpful if an un-filled CNFA is all-zeroes.
+ * In production, though, we only require nstates to be zero.
+ */
+#ifdef REG_DEBUG
+#define ZAPCNFA(cnfa)	memset(&(cnfa), 0, sizeof(cnfa))
+#else
 #define ZAPCNFA(cnfa)	((cnfa).nstates = 0)
+#endif
 #define NULLCNFA(cnfa)	((cnfa).nstates == 0)
 
 /*