Don't ignore white space in string literals in diff display

In the context of a diff, we understand "ignore white space" to mean "ignore changes in white space that are irrelevant in the programs operation. Thus the difference between these two lines is ignored

> var x = "ignore whitespace in strings";

> var x="ignore whitespace in strings";

But a difference in a string literal is significant in any diff.

For an example: 'whitespace' to 'white space'. Thus the diff between these two lines:

> var x = "ignore whitespace in strings";

> var x = "ignore white space in strings";

should be displayed even when "Ignore whitespace" is turned on.