trace: use strbuf for quote_crnl output

When we output GIT_TRACE_SETUP paths, we quote any
meta-characters. But our buffer to hold the result is only
PATH_MAX bytes, and we could double the size of the input
path (if every character needs quoting). We could use a
2*PATH_MAX buffer, if we assume the input will never be more
than PATH_MAX. But it's easier still to just switch to a
strbuf and not worry about whether the input can exceed
PATH_MAX or not.

The original copied the "p2" pointer to "p1", advancing
both. Since this gets rid of "p1", let's also drop "p2",
whose name is now confusing. We can just advance the
original "path" pointer.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

trace.c

@@ -277,25 +277,24 @@ void trace_performance_fl(const char *file, int line, uint64_t nanos,
 
 static const char *quote_crnl(const char *path)
 {
-	static char new_path[PATH_MAX];
-	const char *p2 = path;
-	char *p1 = new_path;
+	static struct strbuf new_path = STRBUF_INIT;
 
 	if (!path)
 		return NULL;
 
-	while (*p2) {
-		switch (*p2) {
-		case '\\': *p1++ = '\\'; *p1++ = '\\'; break;
-		case '\n': *p1++ = '\\'; *p1++ = 'n'; break;
-		case '\r': *p1++ = '\\'; *p1++ = 'r'; break;
+	strbuf_reset(&new_path);
+
+	while (*path) {
+		switch (*path) {
+		case '\\': strbuf_addstr(&new_path, "\\\\"); break;
+		case '\n': strbuf_addstr(&new_path, "\\n"); break;
+		case '\r': strbuf_addstr(&new_path, "\\r"); break;
 		default:
-			*p1++ = *p2;
+			strbuf_addch(&new_path, *path);
 		}
-		p2++;
+		path++;
 	}
-	*p1 = '\0';
-	return new_path;
+	return new_path.buf;
 }
 
 /* FIXME: move prefix to startup_info struct and get rid of this arg */