As I tried to make a full distribution upgrade from Wheezy to Jessie the upgrade of Apache2 didn’t go well at all: dpkg kept coming up with dependencies errors and post-install scripts errors. Unfortunately I don’t have a sample of these errors here. Since I had to dist-upgrade over 30 servers of the same nature I decide to find a solution and here is what I found:

Remove the packages(but not the configurations) that will create problems during the dist-upgrade.
apt-get remove apache2 apache2-mpm-prefork apache2-suexec apache2-utils apache2.2-bin apache2.2-common libapache-mod-security libapache2-mod-fcgid libapache2-mod-php5 libapache2-modsecurity
Add the following default repositories of Jessie in /etc/apt/sources.list
# Debian Jessie
deb jessie/updates main
deb-src jessie/updates main
deb jessie main contrib non-free
deb-src jessie main contrib non-free

apt-get update && apt-get dist-upgrade
apt-get install apache2 apache2-bin apache2-data apache2-mpm-worker apache2-suexec apache2-suexec-pristine apache2-utils libapache2-mod-fcgid libapache2-mod-security2

NOTE: During this upgrade the version of Apache will go from 2.2 to 2.4. This means that some directives of version 2.2 will no more be valid for version 2.4 example:
Oder deny,allow
Should change:
Allow from All >> Require All granted
Deny from All >> Require All denied

See this special Apache site for more information on upgrading Apache 2.2 to 2.4.