Merge branch 'nd/magic-pathspec-from-root'

When giving arguments without "--" disambiguation, object names that come earlier on the command line must not be interpretable as pathspecs and pathspecs that come later on the command line must not be interpretable as object names. Tweak the disambiguation rule so that ":/" (no other string before or after) is always interpreted as a pathspec, to avoid having to say "git cmd -- :/". * nd/magic-pathspec-from-root: grep: avoid accepting ambiguous revision Update :/abc ambiguity check