scmutil: fix requires-file isalnum() check on first byte
Slice instead of subscript to get a bytes from a bytes.
# skip-blame just a py3 slice-instead-of-subscript change
Differential Revision: https://phab.mercurial-scm.org/D2341
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href="{url|urlescape}atom-branches" title="Atom feed for {repo|escape}: branches">
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href="{url|urlescape}rss-branches" title="RSS feed for {repo|escape}: branches">
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<a href="{url|urlescape}log{sessionvars%urlparameter}">changelog</a>
<a href="{url|urlescape}shortlog{sessionvars%urlparameter}">shortlog</a>
<a href="{url|urlescape}graph{sessionvars%urlparameter}">graph</a>
<a href="{url|urlescape}tags{sessionvars%urlparameter}">tags</a>
<a href="{url|urlescape}file{sessionvars%urlparameter}">files</a>
<a href="{url|urlescape}help{sessionvars%urlparameter}">help</a>
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<a type="application/atom+xml" href="{url|urlescape}atom-branches">atom</a>
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<h2><a href="/">Mercurial</a> {pathdef%breadcrumb} / branches</h2>
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