histedit-test: rename histedit-revspec into histedit-argument
We have no testing for argument. This small file seems perfect once but needs a
rename.
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$ hg init
$ echo '[Section]' >> $HGRCPATH
$ echo 'KeY = Case Sensitive' >> $HGRCPATH
$ echo 'key = lower case' >> $HGRCPATH
$ hg showconfig Section
Section.KeY=Case Sensitive
Section.key=lower case