Improve autocompletion behavior

[ptzz]

Typing z dev in the example below will show the matching list and also autoexpand the z argument to my home directory in the next prompt, waiting for more input. However, there is no way to quickly select one of the alternatives with the home dir autocompletion in the way (unless knowing the full path, which with z I shouldn't really need to know)

~$ z de
dev/         testdata/    third_party/
~$ z /Users/xxx/

Say I want to go to the third_party directory at this point (it's in /Users/xxx/dev/some/long/subpath/thirdpaty). Removing the the autocompleted home dir part and typing z third_party is probably the fastest with the current z behavior.

Maybe inserting the common matching dir could simply be removed?

Btw I have set show-all-if-ambiguous on is set in .inputrc, that's why the options show up when pressing tab key.

[mrjohannchang]

@ptzz please check this out and see if it helps.