Fixes CRM-19306: Fix documentation for upload directories in civicrm.…

[ergonlogic]

…settings.php template.

Fixes: https://issues.civicrm.org/jira/browse/CRM-19306.

[civicrm-builder]

Can one of the admins verify this patch?

[totten]

jenkins, ok to test

[totten]

Review notes:

• The reported test failure (CivicrmUpgradeTest.4_2_9-multilingual_af_bg_en_mysql_bz2) is a pre-existing problem.
• Verified that that there is a cleanup logic which deletes uploadDir and could not find similar logic for customFileUploadDir.
• Grepping for >cleanup(, I could only find one use case (doSiteMove()) which would actually delete uploadDir, so it may be particularly temporary in practice.
• Between the two, agree that uploadDir is more temporary, so this seems like an improvement. Merging.

Thanks, Chris!