revlog: don't try to partialmatch strings those length > 40 _partialmatch() does prefix matching against nodes. String passed to _partialmetch() actualy may be any string, not prefix only. For example, "e410be8603932e46a51298748a4b874739037fad or 300" is a good argument for _partialmatch(). When _partialmatch() searches using radix tree, index_partialmatch() C function shouldn't try to match too long strings.

--- a/mercurial/parsers.c	Sat Aug 11 12:45:37 2012 -0500
+++ b/mercurial/parsers.c	Thu Aug 02 19:10:45 2012 +0400
@@ -1084,8 +1084,10 @@
 		return NULL;
 	}
 
-	if (nodelen > 40)
-		nodelen = 40;
+	if (nodelen > 40) {
+		PyErr_SetString(PyExc_ValueError, "key too long");
+		return NULL;
+	}
 
 	for (i = 0; i < nodelen; i++)
 		hexdigit(node, i);