Use a single statement for DataMapper truncation on PostgreSQL.

This change aligns the behavior of the DM PostgreSQL truncation adapter with
the ActiveRecord one. A single statement is faster and safer than lots of
`TRUNCATE TABLE ... CASCADE` statements.

While this commit only implements single statements for PostgreSQL, it
provides the extension point necessary for other adapters to switch to single
statements in the future.
Support Oracle JDBC Adapter
Oracle does not support semi-colons in TRUNCATE TABLE statements and throws an `ORA-00911: invalid character` error. So use the same syntax with a JdbcOracleConnection as used by the OracleEnhancedAdapter.
fixes Rakefile...
Fixing minor typo due to a case error in README
Merge pull request #250 from navinpeiris/patch-1

Fixing minor typo due to a case error in README
Transactions should not be joinable
Use respond_to? with true to check inspect private/protected methods
Merge pull request #119 from rsutphin/dm-pg-single-trunc

Use a single statement for DataMapper truncation on PostgreSQL
Merge pull request #254 from TMXCredit/master

Use respond_to? with true to check inspect private/protected methods
Changes to get specs to green.  Remove Ruby version related dotfiles to allow use of multiple Ruby versions
Merge pull request #253 from chancancode/non_joinable_transactions

Transactions should not be joinable
Merge pull request #255 from petergoldstein/feature/get_specs_to_green

Fix specs, remove Ruby dotfiles
Merge pull request #249 from avinmathew/master

Support Oracle JDBC Adapter
switch from Before/After cucumber hooks to Around with #cleaning
Merge remote-tracking branch 'origin/master' into cleaning
some tests for #cleaning
document DatabaseCleaner.cleaning and usage with around filters in cucumber / rspec / minitest