doc/tutorial: use RequestContext instead of Context

https://docs.djangoproject.com/en/dev/intro/tutorial03/#write-views-that-actually-do-something
The first real view in the tutorial is using Context which results in two problems:

 * the comparison with the render shortcut is incorrect  
   render uses RequestContext which makes the verbose example not equal to the shortcut  
   the render shortcut is documented in the paragraph below the verbose example
 * new django users that were enticed to use the verbose example would later have problems with static files etc.  
   I've seen a few cases of this on #django