The previous one reportedly ended up escaping 't' to '\t' in some
setups (at least bash 3.2.48 on OS X 10.6, but not with 4.1.7 on
Fedora nor 3.2.25 on CentOS), probably due to missing backslash in the
regex. This one removes some spurious escaping and duplicates in the
char class, and should communicate the intent better.
Turn it on dynamically when needed instead; see doc/styleguide.txt for
a longer explanation. This fixes many non-filename completions which
had been previously more or less broken due to unwanted
escape-as-filenames behavior.
