Fixed raw query with ForeignKey field.

- Added test for fixed bug (removed duplicate test)
Fixed selection of individual tests on command line.

It is more important than specifying the order of test cases (the order will
be undefined after this fix).
Modified tests to be independent on no/installed Person Account. (part 1)

Part 1: Only renamed all "Account" to "Contact" in test_integration.py
        (to be part 2 smaller and more readable)
Modified tests to be independent on no/installed Person Account. (part 2)

Part 2: Fixed tests after simple replacement Account by Contact.
- The added field "Company" in Lead is required by my Salesforce db.
- Username is read from settings instead of hardcoded email.
- Fixed previously skipped tests of DateTime fields.
Added tox configuration for automated tests with different virtual environments.

Cosmetic updates in settings.
Fixed reading DateTimeField for Django 1.3

Fixed Django 1.5 warning about admin media.
Fixed reading DateTimeField for values with milisecond resolution.

Previously it raised ValueError. Added test.
Fixed all tests to restore db status before Assert

It is safer because future tests will not be breaken if the assert fails.
Added support for Django 1.6b1

- Requires new manage.py,
- Django 1.6 SQLCompiler has some modified methods and attributes
- More parameters to field_cast_sql
Added support for Django 1.6b2

Created an empty driver that emulates parts of DB API2 required by Django 1.6.
It should also define some Error classes.
Fixed TimeField for read and save.

This previously raised a ValueError. Added test.
Added support for read only fields like Lead.Name or LastModifiedBy.

These fields can be used in the model with the parameter
`sf_read_only=models.READ_ONLY`, but the backend knows the field shouldn't be
saved. Previously the field couldn't be used in the model or that model
couldn't be saved.
Added tests for read only fields.
Added a customized inspectdb command for salesforce backend.

The command 'python manage.py inspectdb --database=salesforce' exports
a complete valid structure of Salesforce database for models.py that can
be used unmodified to read and write all retriveable objects, including
recognition of relations between them or read only fields recognition.
Added hynekcer to AUTHORS list
updates primarily to the tests, and testsrunner

(Rebased to the rurrent branch and splitted to more commits by hynekcer.)
Improvement to query delete for nested WhereNodes.

(Rebased to the current branch and splitted to more commits by hynekcer.)
Some code from sbussetti's commit is omitted because not actual in this branch.
Fixed switch PERSON_ACCOUNT_ACTIVATED for it not activated
Added warning for unsupported values of on_delete
Fixed operators LIKE '%...%' and similar