perf: define util.safehasattr forcibly for Mercurial earlier than 1.9.3 Before this patch, using util.safehasattr() prevents perf.py from being loaded by Mercurial earlier than 1.9.3 (or 94b200a11cf7), because util.safehasattr() isn't available in such Mercurial, even though there are some code paths for Mercurial earlier than 1.9.3. For example, setting "_prereadsize" attribute in perfindex() and perfnodelookup() is effective only with Mercurial earlier than 1.8 (or 61c9bc3da402). This patch is a preparation for using util.safehasattr() safely in subsequent patches. This patch defines util.safehasattr() forcibly without examining whether it is available or not, because: - examining existence of "safehasattr" safely itself needs similar logic - safehasattr() is small enough to define locally