Unquote values of requested variables

If a --variable is requested, make sure to remove the quoting since it's
likely the value will be used verbatim in shell command substitution. If
the quotes remain in the value, they'd get embedded in the shell
variable, too.

Freedesktop #67904 (https://bugs.freedesktop.org/show_bug.cgi?id=67904)
Add missing options to manual

Freedesktop #66155 (https://bugs.freedesktop.org/show_bug.cgi?id=66155)