fix conflicting fai packages
fix install new xivo-fai
add wheezy upgrade notice

Conflicts:

	xivo-upgrade/bin/real-xivo-upgrade
update preseed file location
run PG migration before changing the distribution

reason: PG migration need packages from either the wheezy
distribution, or squeeze-xivo-skaro. When it was done, there was none
of those distributions in the sources.list.
install non-PAE linux image if PAE failed to install
display notice at the end of Wheezy upgrade
add newline before notice
fix is_linux_3.2_installed
add step to wheezy upgrade before dist-upgrade
downgrade postgresql-common if necessary
make GRUB warning more imposing
add grub check before upgrade
improve xivo-fai clean

reason: avoid removing xivo-fai{,-dev} when removing old fai package
fix package name extraction command
add command to force the regeneration of grub config file
fix command to extract old fai package names
add reboot step after installing grub 2
move grub check after the upgrade

fixing grub before the upgrade does not fix grub
move grub check at the end of the upgrade