Fix bug reported by Roger Peppe, namely that

	regexec(regcomp("^good"), "hello\ngoodbye", nil, 0) == 0

The code to skip forward line by line when matching
a pattern beginning with ^ was off by one in regexec.c.

I changed rregexec.c to use the new(er than libregexp)
runestrchr function so that it looks more like regexec.

Reference: /n/sources/patch/applied/regexec
Date: Fri May 18 18:50:59 CES 2007
Signed-off-by: rsc@swtch.com

--- /sys/src/libregexp/regexec.c	Fri May 18 18:49:19 2007
+++ /sys/src/libregexp/regexec.c	Fri May 18 18:49:19 2007
@@ -59,7 +59,7 @@
 				p = utfrune(s, '\n');
 				if(p == 0 || s == j->eol)
 					return match;
-				s = p;
+				s = p+1;
 				break;
 			}
 		}
--- /sys/src/libregexp/rregexec.c	Fri May 18 18:49:21 2007
+++ /sys/src/libregexp/rregexec.c	Fri May 18 18:49:21 2007
@@ -26,6 +26,7 @@
 	Relist* tle;		/* ends of this and next list */
 	Relist* nle;
 	int match;
+	Rune *p;
 
 	match = 0;
 	checkstart = j->startchar;
@@ -40,25 +41,22 @@
 	/* Execute machine once for each character, including terminal NUL */
 	s = j->rstarts;
 	do{
-
 		/* fast check for first char */
 		if(checkstart) {
 			switch(j->starttype) {
 			case RUNE:
-				while(*s != j->startchar) {
-					if(*s == 0 || s == j->reol)
-						return match;
-					s++;
-				}
+				p = runestrchr(s, j->startchar);
+				if(p == 0 || s == j->reol)
+					return match;
+				s = p;
 				break;
 			case BOL:
 				if(s == bol)
 					break;
-				while(*s != '\n') {
-					if(*s == 0 || s == j->reol)
-						return match;
-					s++;
-				}
+				p = runestrchr(s, '\n');
+				if(p == 0 || s == j->reol)
+					return match;
+				s = p+1;
 				break;
 			}
 		}