Fix PostgreSQL sequence creation error

[SoKnight]

Sometimes, when application starts again (not firstly) and tries to create non-existing tables, then executing SQL sequences without IF NOT EXISTS flag that causes an exception (see a screenshot below).

[noordawod]

Thanks @SoKnight, LGTM 🎉 What do you think, @j256?

[SoKnight]

I compiled ORMLite JDBC jar from sources forked by me and test it.
It's working fine, see a screenshot :)

[Bo98]

I don't think isCreateIfNotExistsSupported() is the correct check here. It checks if CREATE TABLE IF NOT EXISTS is supported, which is PostgreSQL 9.1 and later. CREATE SEQUENCE IF NOT EXISTS however is only supported in 9.5+.

[SoKnight]

I don't think isCreateIfNotExistsSupported() is the correct check here. It checks if CREATE TABLE IF NOT EXISTS is supported, which is PostgreSQL 9.1 and later. CREATE SEQUENCE IF NOT EXISTS however is only supported in 9.5+.

Oh yes, sure, it's very important, lol...