bundle update AR + add simplecov gem

This will work for jruby 1.7 and greater
To run with COVERAGE variable set to true
COVERAGE=true rake test_mssql
update appraisal gemfiles rails versions
adapter.jar needed to be rebuild
explain support for H2 and HSQLDB
re-arrange the explain tests so they could be shared
no need to define PostgreSQLAdapter as it's removed
bellow using `remove_const(:PostgreSQLAdapter)`
hacks with LOADED_FEATURES belong to adapter code
re-arrange (shared) test helper code into a test_helper.rb
DB2 becomes a first-class citizen (adapter)
mock zos? method as it was erroring tests
correct DB2 schema selection (when as400 url has parameters)
[DB2] cache #zos?, #as400? and #db2_schema methods
add WITH statement tests for DB2 and Postgres (for now)
[postgres] bug in create_database without options (fixes #306)
Only include jTDS build on Java 7
Add additional point to driver versions
[oracle] support jdbcoracle adapter name
review test db setup - notes no longer relevant for latest XE
separate out Postgres test that do not need a DB 
+ update WITH test
support running single test file on 1.8 (require 'rubygems')
separate out DB2 test that does no require a DB
expose select? and insert? helpers on JdbcAdapter class
[oracle] should support WITH statements (as well)