lib/re1.5: Distinguish between subject start-of-line and start-of-srch.

Otherwise a repeated sub/split will continue to match ^ to the start of
that search.

Signed-off-by: Damien George <damien@micropython.org>

lib/re1.5/re1.5.h

@@ -130,6 +130,7 @@ Sub *update(Sub*, int, const char*);
 void decref(Sub*);
 
 struct Subject {
+	const char *begin_line;
 	const char *begin;
 	const char *end;
 };

lib/re1.5/recursiveloop.c

@@ -68,7 +68,7 @@ recursiveloop(char *pc, const char *sp, Subject *input, const char **subp, int n
 			subp[off] = old;
 			return 0;
 		case Bol:
-			if(sp != input->begin)
+			if(sp != input->begin_line)
 				return 0;
 			continue;
 		case Eol: