Re: [1.8.0] use 'stage' term consistently

Jonathan Nieder wrote:

For the command-line interface:

Making the "git stage" command more prominent. Unfortunately it is currently a synonym for "git add", which makes "git rm" less discoverable and generally isn't very helpful. But if we discard that property, it could become a nice way to make some operations more discoverable:

	git stage --add <paths>; # stage an addition
	git stage --remove <paths>; # stage a removal
	git stage --edit <paths>; # edit the staged content
	git stage --apply <patch>; # stage the described change

These would be commands that modify the index without touching the worktree.

If anyone claims this is the command for manipulating "the stage", we can apologize for the confusing homonym and point them to a dictionary and images of raised platforms and staging areas and hopefully that will avoid any confusion. The command is named after the verb.

Finding a better mnemonic than "also update the current directory cache" and "trust the current directory cache" for operations like git apply --index and git grep --cached. Better concepts would be "search the content staged for the next commit" and "also update the staged content".

Maybe:

	git apply --index=(yes | no | only)
		# apply         	= apply --index=no
		# apply --index 	= apply --index=yes
		# apply --cached	= apply --index=only

	git grep --index; # (= git grep --cached)

I imagine others can come up with something better.