Be more wary in initdb's creation of platform-dependent collations.

Discard any collation aliases that match the built-in pg_collation entries
(ie, "default", "C", "POSIX").  Such aliases would be refused by a CREATE
COLLATION command, but since initdb is injecting them via a simple INSERT,
it has to make the corresponding check for itself.  Per Martin Pitt's
report of funny behavior in a machine that had a bogus "C.UTF-8" locale.

Also, use E'' syntax for the output of escape_quotes, as per its header
comment.