Fix#332.
This adds a new "PreValidate" hook that is executed before checking
the backup location. This allows, for example, mounting a remote
source to make the directories of the location available.
"PreValidate" is added as a new hook to avoid any breakage that might
have been caused by changing the behaviour of the "before" hook.
Documentataion updates included.
ಠ_ಠandGitHub
Stuart HickinbottomandGitHub
Alexander ZhangandGitHub
Christoph LoyandGitHub
Skye JandGitHub
cupcakearmyandGitHub