Merge pull request #545 from irskep/fix_json_error

mrjob.conf aliases JSONDecodeError to ValueError if not using simplejson. Fixes #544.
added a test for HadoopJobRunner.path_exists() (it fails, as expected)
fixed HadoopJobRunner.path_exists()
Merge pull request #553 from davidmarin/path_doesnt_not_exist

Fix HadoopJobRunner.path_exists() (Issue #549)
just use ValueError, rather than the simplejson-specific JSONDecodeError
Merge pull request #555 from davidmarin/just_use_value_error

Just use value error
improving test case coverage for fs methods
Fix pointlessly broken test case, probably from a botched merge resolution
Fix S3 mocking in a couple of places where it was missed due to env vars in devs' envs
Merge branch 'master' into fs_tests
update __credits__ to include reno bowen and tom dooner
Fix for "unexpected ls line from hadoop" exception.

When using s3n:// urls the `hadoop.ls()` method threw an exception
as the output was not in the expected format.
Syntax errors (doh!)
Consolidate emr-concepts and emr-config into emr-quickstart, stub out a new section for runner basics
EMR quickstart
Add CONTRIBUTING.rst
re-add .gitignore
Re-wording and extra title
Merge pull request #566 from irskep/emr-quickstart-docs

Simple EMR quickstart docs
Merged release 0.3.5 into master