Escaping with backslash(\) in variable strings cannot be done for backslash itself

[olofhagsand]

In cligen variables, such as in the spec:

  s <string>;

escaping with backslash is used for eg ? which have other meanings. That is:

  cli> s x\?y

produces the string "x?y" and not query.
However, escaping backslash itself does not work properly:

  cli> s x\\y

produces the string "xy", while it should produce "x\y"