Reverted r1412 to allow hiding command entry on focus lost; src/textadept.c
If command_entry_completion handles keys first, pressing "Tab" after showing
completions switches focus to Scintilla without propagating the key.
If command_entry handles keys first, pressing "Enter" in the completion list
will be incorrectly interpreted as a normal "Enter" press.
Reverted to using the "activate" signal to interpret "Enter" so command_entry
can handle keys first, keeping "Tab" from switching focus.
Allow empty tables as keychains if they have metatables; core/keys.lua