	Switch to a topic branch.  You can use 'git checkout <branch>'
	to get the same effect, but this command helps you navigate
	the dependency graph, or allows you to match the topic branch
	name using a regular expression, so it can be more convenient.

	There following subcommands are available:

	    'tg checkout push'    Check out a branch that directly
	    		       	  depends on your current branch.

	    'tg checkout pop'     Check out a branch that this branch
	    		       	  directly depends on.

	    'tg checkout goto <pattern>'  Check out a topic branch that
	    		          matches <pattern>.  <pattern> is used as
	    		          a sed pattern to filter all the
	    		          topic branches.

	    'tg checkout next'    An alias for 'push'.
	    'tg checkout child'   An alias for 'push'.
	    'tg checkout'      	  An alias for 'push'.

	    'tg checkout prev'    An alias for 'pop'.
	    'tg checkout parent'  An alias for 'pop'.
	    'tg checkout ..'      An alias for 'pop'.

	If any of the above commands can find more than one possible
	branch to switch to, you will be presented with the matches
	and ask to select one of them.

	The <pattern> of 'tg checkout goto' is optional.  If you don't
	supply it, all the available topic branches are listed and you
	can select one of them.

	Normally, the 'push' and 'pop' commands moves one step in
	the dependency graph of the topic branches.  The '-a' option
	causes them (and their aliases) to move as far as possible.
	That is, 'tg checkout push -a' moves to a topic branch that
	depends (directly or indirectly) on the current branch and
	that no other branch depends on.  'tg checkout pop -a'
	moves to a regular branch that the current topic branch
	depends on (directly or indirectly).  If there is more than
	one possibility, you will be prompted for your selection.

