Stop creating SQL literals for aliases.

[ernie]

PostgreSQL requires that the aliases aren't quoted, but MySQL and SQLite
don't seem to care at all, and it seems like we would do better to avoid
creating SqlLiteral nodes where we don't need to.

I ran the mysql/postgresql/sqlite3 tests for ActiveRecord against this
branch and everything passes. Of course, we all know that doesn't
necessarily mean anything.

This is tangentially related to activerecord-hackery/squeel#246, but still doesn't
address the "reserved word" complaint there. Might make sense to have an
Alias node for special visitation vs the SqlLiteral one, perhaps. Or
maybe we just don't care if someone wants to alias things using reserved
words in pg, because that's just cray-cray.

[ernie]

@tenderlove Pinging you for thoughts here. Seems like a moderately risky thing to do and I'd rather not be the only eyes on it.

[tenderlove]

If the other dbs pass, then

[ernie]

@tenderlove If, by "other DBs", you mean frontbase, oracle, etc, well then I'm gonna need to ping some other folks, as I don't have them running here. Otherwise, this was verified with MySQL, PostgreSQL, and SQLite3, using rake test.

[matthewd]

@ernie err, PostgreSQL is entirely happy with quoted aliases... they just have to be using "identifier" quotes, not 'string literal' quotes. And without actually going and checking the standard, I bet that's the defined behaviour (and thus the more likely to work on other platforms).

[tamird]

@ernie, is this still relevant? needs a rebase if so

[kbrock]

@ernie Is this still relevant?
Were you thinking of going with " instead of '?
That would avoid the whole "how do I tell the library I actually want to quote this" dilemma.

[matthewd]

Per #523, Arel development is moving to rails/rails.

If this PR is still relevant, please consider reopening it over there.