sh script's STAMPFILE loses mktemp safety

[MAProsper]

mktemp guaranties to create the STAMPFILE without clobbering other files. However the file gets deleted and manually created with touch in the remove_cmd function, losing it uniqueness guaranties.

This could be fix by calling rm -f "$STAMPFILE" at the end of the script and not remove it in remove_cmd. This also has the benefit of being more performant (since the file is not recreated constantly) and also it ensures that the stamp file is always deleted (even if remove_cmd is not called).