Update workaround for '--follow' log argument with largefiles extension.

*hg bug for largefiles was fixed in hg 2.7, so workaround not needed anymore for later versions;
*history tests try to  fix - largefiles extension is switched on for windows by default
Delete unused file with a lot of bugs.

*see the same functionality in HgLogCommand and HgUtil.
simplify API — TextBrowseFolderListener
JSDebug settings editor — file chooser must use the same logic as RC producer