Consider colons as a token separator

I bumped into tokenization problems on PostgreSQL with statements of the form:
CREATE TABLE base_table (
    base_table_id integer DEFAULT nextval('base_table_seq'::regclass) NOT NULL
);
The parser considers "'base_table_seq'::regclass" to be a full token, but it should be considered as 2 tokens:
"'base_catalog_table_seq'" and "regclass"

Now I haven't tested this with other rdbms and I'm not sure this should be applied to all of them.
Merge pull request #23 from pmalouin/patch-1

Consider colons as a token separator