Correcting link syntax in Tutorial.pod

The link was missing a pipe (|) separator and was using a '/' in the link
text, which is disallowed by the POD formatting rules.  I've removed the
leading "t/" in the link text and hope that this is OK.  The sense of the
sentence is retained, the reader merely needs to know to look in the 't'
directory for the 900_run_features.t file.
Removing $_ modifications in list functions

According to PBP, modifying $_ within map, grep or first is *really* not a
good idea, since $_ gets aliased within the list function, thus unexpected
things can occur.  One recommendation in PBP is to simply modify a copy of
each list element and thus avoid the problem (this is the solution presented
in this commit).  Alternatively, one could rewrite the map/grep/first as a
for loop, thus making the side-effects more explicit.  Here is how that
would look in _build_transformed_matches():

my @newly_transformed_matches;
for my $match ( @transformed_matches ) {
    push @newly_transformed_matches, $self->transform( $match );
}
@transformed_matches = @newly_transformed_matches;

This does the same thing (i.e. the tests pass, and Devel::Cover tells me
that the code is exercised by the tests) and may be more
readable/maintainable depending upon one's point of view.
Make the dependency a little more explicit