This adds tab completion to textinput components. They can be configured
with a completion function. This function is called when the user
presses <tab>. The first completion is initially shown to the user
inserted into the text. Repeated presses of <tab> or <backtab> cycle
through the completions list. The completions list is invalidated when
any other non-tab-like key is pressed.
Also changed is some logic for current completion generation so that
all available commands are returned when <tab> is pressed with no
current text and similarly for arguments of commands.
This command allows the user to change tab by giving the tab name. This
can be tab completed too. The previous tab is stored in the tabs module
so that when a new tab is created it is still possible to go to the
previous one.
Normal invocation is :ct folder
Previous tab is :ct -
