#938336 by greg.1.anderson: propagate Drupal site context options (local or remote) into aliases used with sql-sync.

Don't return FALSE from a validate hook unless we really mean it. It matters now. drush_pm_updatecode_validate().

#1010984 by greg.1.anderson: Allow aliases to define command-specific options that only apply when alias is used as source or target of rsync / sql-sync

#1008118 by greg.1.anderson: Standardize on 'return drush_user_abort();' as correct way to stop execution when user cancels

Get rid if minimally helpful error message 'An error occurred at function : '. Lets trust our commands to set descriptive error messages.

Fatal error: Call to undefined function conf_path() in /Users/mw/c/h/drush/includes/environment.inc on line 790

Call Stack:
    0.3726     735000   1. {main}() /Users/mw/c/h/drush/drush.php:0
    0.4013    3209200   2. drush_main() /Users/mw/c/h/drush/drush.php:42
    0.4889    6885856   3. drush_dispatch(???, ???) /Users/mw/c/h/drush/drush.php:102
    0.4890    6886168   4. call_user_func_array(???, ???) /Users/mw/c/h/drush/includes/command.inc:196
    0.4890    6886504   5. drush_command(???) /Users/mw/c/h/drush/includes/command.inc:0
    0.4895    6891456   6. call_user_func_array(???, ???) /Users/mw/c/h/drush/includes/command.inc:694
    0.4895    6891488   7. drush_invoke(???, ???) /Users/mw/c/h/drush/includes/command.inc:0
    0.4904    6904280   8. call_user_func_array(???, ???) /Users/mw/c/h/drush/includes/command.inc:110
    0.4904    6904616   9. drush_core_drupal_directory(???) /Users/mw/c/h/drush/includes/command.inc:0
    0.4904    6904616  10. _drush_core_directory(???) /Users/mw/c/h/drush/commands/core/core.drush.inc:708
    0.4904    6904664  11. drush_bootstrap(???, ???) /Users/mw/c/h/drush/commands/core/core.drush.inc:686
    0.4928    6907128  12. drush_bootstrap_validate(???) /Users/mw/c/h/drush/includes/environment.inc:191
    0.4929    6907448  13. _drush_bootstrap_drupal_site_validate() /Users/mw/c/h/drush/includes/environment.inc:270 work on D7.

Update site-upgrade for recent changes in pm code. I removed a cache clear from updatedb on D7. We should be on the lookout for ill consequences.