Changed the location of the pre and post scripts

Based on the (1) and (2), the locations for scripts that are run by another program belong in /usr/libexec

(1) http://www.linuxbase.org/betaspecs/fhs/fhs.html#usrlibexec
(2) http://fedoraproject.org/wiki/How_to_create_an_RPM_package#Macros