Made rqworker and rqinfo respect db parameters from --url

When starting the rqworker and rqinfo scripts with an --url parameter containing a non default database, e.g. redis://localhost:6379/2, both scripts connected db 0 instead of the desired database. Fixed this behavior by ignoring the --host, --port and --db arguments if --url is there.

Also fixed another issue with the rqinfo script, in which it defaulted to only the 'default' queue instead of finding all available queues using Queue.all().
First stab at writing implementing job dependency.
Don't enqueue waitlisted jobs on failed execution.
Merge pull request #198 from johannth/scripts-respect-url

Made rqworker and rqinfo respect db parameters from --url
extract `safe_fetch_job` method
get a page of jobs
Minor refactoring of the paging logic.
Fix typo.
Update changelog.
Replace the Calculator fixture by a Number fixture.

This makes the tests a little more realistic, since I want to add a test
for class methods.
Add explicit classmethod test.
Avoid race conditions when enqueueing job with dependency.
Simplify enqueue_waitlist by using lpop.
Internally renamed the term "parent" to "dependency".
Merge branch 'master' of git://github.com/nvie/rq into job_dependency

Conflicts:
	rq/queue.py
Don't fail if job dependency is modified during enqueue process.
Writes an optional specified PID file on startup
take REDIS_URL from settings if exists
Fix a problem caused when a nonstandard stdout is defined and not
properly implemented
Ok i am being lazy using the try catch