#992554 by greg.1.anderson: Improve drush function names for functions where drush calls back in to drush

#992170 by greg.1.anderson: Fix accidental change to drush_shell_exec return code, and fix comment so that it maches historic usage of the function

#985716 by wapnik: Turn off notices when calling _drush_site_install6_cookies to avoid junk in the output stream (cookie values)

#781040 by jonhattan: VCSs integration: remove current project files prior to updating to new release and remove orphan directories afterwards.

#983222 by pcambra, greg.1.anderson: Custom code to work with update services and make pm-releases and pm-releasenotes work without a bootstrapped site; Shared behaviour with pm-download. Filter releases by relevance. Clean up of pm-releasenotes. Introduce DRUSH_BOOTSTRAP_MAX. Suggest releases to download when there is no recommended release.