For some reason Ubuntu's version of screen includes timestamps in the
output of `screen -list`. The timestamps aren't present on other
distributions (tested on Fedora and Arch Linux), nor when building from
source. This commit fixes the regex so that with or without the
timestamp, fish will correctly show suggestions for screen sessions.
Fixes some potentially unsafe uses of direct substitution into regex
expressions and also switches some completions to regex-based now that
there is a safe way of using it.
* fixes broken completion of screen on osx, test on ubuntu and mac with fish 2.3.1
* replaces sed, __fish_sgrep with fish builtin string
* add completion for `screen -x`
* adjust format (e.g. 12345.socket\t01/01/16 09:55:00 Detached)
