Do not escape '=' when printing value names with the "values" subcommand

[ipkiss42]

Escaping is undesirable for the "values" subcommand, since there is no possible ambiguity in its output (no tag=value is printed). It was also not consistent.

Behavior before the fix:

$ tmsu tag . 'foo=a\=b' 
tmsu: new value 'a=b'
$ tmsu values foo
a\=b
$ tmsu values
a=b

Note that formatTagValueName (used in imply and tags) still escapes =.