Fixes #1973

Failure in Firefox when record id equals 'watch' .
Gecko adds watch function to Object.prototype (as described here:
https://developer.mozilla.org/ru/docs/Web/JavaScript/Reference/Global_Ob
jects/Object/watch)
add checking if Object.prototype.watch is exist

Object.prototype.watch function is used in model unit test to check a
collision of a record's id with object function's name.
So we create this function if needed and remove after test if it was
not defined before.
Merge pull request #1990 from eljusto/master

Fixes #1973