Merge pull request #81 from nsoranzo/objects_cleanup

ObjHistoryClient and ObjDatasetClient cleanup
Small docfix in ToolShedInstance.
Fix url joining problem described in issue #82.
Add histories.download_dataset test case.
Fix the check if the default bucket is set when the user data is being composed
Update version
Bump to dev version
added note on wait time to Workflow.run
fix for #85
Added changelog file (with entries for the most recent, v0.5.1, release)
Remove from ObjLibraryClient 6 methods which should be called from Library instances (objects cleanup).
Add documentation for upload_file() and paste_content() methods. Make upload_payload() method private.
Rename get_current_history() to get_most_recently_used_history().

The current history is not necessarily the most recently used one.
The Galaxy API method to get the current history has been removed in commit

https://bitbucket.org/galaxy/galaxy-central/commits/5ce55f9f2923dcdf27150cce3addd6e1ff3782d7