Fix using alias in DATE_ADD

[eigan]

Same changes as in pull #230 and issue #218 for DateDiff.

Tests will probably fail in Doctrine 2.2 like #239.

[stevelacey]

Hm, why haven't the tests ran... dammit Travis

[stevelacey]

@eigan any progress with these two PR's? tests are failing

[eigan]

I will take a look this weekend @stevelacey

[eigan]

Tests only fails with Doctrine 2.1.*. And looks to be something about not finding 'alternative' (the alias).

The 2.2 blog post mentions something about alias. This commit was added to 2.2 and has adjustments to SqlWalker..

Do you know anything regarding alias and Doctrine 2.1?

[stevelacey]

@eigan looks like aliases weren't supported in 2.1 – it's probably acceptable to check the Doctrine version and early return at the start of your test if <2.2

[eigan]

@stevelacey Marked test as skipped in < 2.2

[stevelacey]

@eigan thanks for your contribution 😄