topics: rename '--change' flag to '--rev' flag
The --change flag was used to read a revset of which topic should be changed. In
mercurial we use --rev for this type of flag.
Now things will work as follows:
`hg topics topicname`: It will set the current topic
`hg topics topicname --rev revset`: Change topic of all the revs in the revset
to topicname
Further patches will try to achieve the following:
`hg topics --clear --rev revset`: clear topic from all the revisions in the
revset
`hg topics --clear`: clear the current topic (Current behavior)
`hg topics --rev revset`: show topics on the revisions in the revset