Rename "request pull" to pull request
    
    People are used to the "pull request" name, use it instead,
    "request pull" is confusing and brought major language issues
    in most cases.
    
    As this is more or less a text fix, also fixed a typo on
    issues page (s/on/of in open/closed issues bar) and reworded it
    to sound a bit better.
    
    Merges: #2144