revlog: zlib.error sent to the user (issue3424)

Give the user the zlib error message instead of a backtrace when decompression
fails.

mercurial/revlog.py

@@ -112,7 +112,10 b' def decompress(bin):'
     if t == '\0':
         return bin
     if t == 'x':
-        return _decompress(bin)
+        try:
+            return _decompress(bin)
+        except zlib.error, e:
+            raise RevlogError(_("revlog decompress error: %s") % str(e))
     if t == 'u':
         return bin[1:]
     raise RevlogError(_("unknown compression type %r") % t)