When doing two-way variable replacement, if the variable has a Windows
path (i.e. backslashes) also do a match for the value with forward slashes.
In other words, if a path `Y:/shared/...` comes in, and the variable value
is (correctly) `Y:\shared\...`, it will be seen as a match.
Backslashes can be included in two ways, as-is (which works fine) and
between double quotes (in which case they need escaping). This test checks
for both.