rewriteutil: use precheck from core if recent enough
This commit makes the evolve extension's `rewriteutil.precheck()` simply delegate to the same function from Mercurial core, if that function is deemed recent enough. The way I made that check is by looking for `rewriteutil.find_new_divergence_from()`. That means that there's a range of commits (ba6881c6::8125bcd2^) where the user would see less detailed error messages if they are running with an hg version from that range (there are no released versions in that range). As you can see in the tests, switching to core's version of the function mostly affects error messages and exit codes.
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