WordPress requires exec() command not be disabled

I came across this problem recently when upgrading a site which was working fine from 4.6.x to 4.7.8. Immediately I noticed that the KCFinder file browser window was not functioning as it should, and I could neither upload nor browse files on the server. I posted a question on the Stack Exchange site: http://civicrm.stackexchange.com/questions/12303/kcfinder-browser-shows-empty-pop-up-window-how-to-debug which includes details of what was appearing in the error log when attempting to browse files.
I proceed to remove Civi 4.7.8 form this site and instead installed 4.6.18, which does not display the same issue and works as expected.
So while this may not be a bug per se, 4.7.x clearly has different requirements of the hosting server, which in my case were not being met, so rather than invest time which I don't have in the hope of being able to identify what's stopping 4.7.8 from working properly on my Debian server (MySQL 5.5, PHP 5.6, Apache 2.2) I simply opted to downgrade to 4.6.18 and post this issue in the sure expectation that someone far more knowledgable than I in these matters will be able to clarify what the issue is, (hopefully my error log will be of value), and either make suitable changes to the 4.7 series or clarify what that changed server environment requirements are.