Trying to kill install-utils.inc/old install crap:

Trying to kill install-utils.inc/old install crap:
* Cripple the old installer (entry point is gone, supporting code immediately exits). Keeping the latter for reference still :)
* Move posix_isatty() wrapper to Maintenance.php, all CLI scripts include this
* Clarify docs on archive() deprecation and removal - hasn't been used going back thru 1.15
* Clarify docs on dbsource() deprecation and removal - was in wide use thru 1.15. 1.16 removed all extension usages
* Move the two PHP bug tests to a file with the other installer files, moved them to more logical places in new install/update sequence
* Remove mw_have_dl/mw_get_session_save_path, zero callers
* Move readconsole() and helpers to be a static method on Maintenance, no extensions have used it since 1.15 either