also explicitly use our own giflib and libtiff.

so that we don't need to differentiate software/erp5/software.cfg in erp5-component branch.

zc.buildout >= 1.6.0-dev-SlapOS-013 automatically rebuilds parts whose referring parts are modified.

Conflicts:
	component/apache/buildout.cfg
	stack/monitor/buildout.cfg

apache-frontend: update documentation for per frontend configuration

(cherry picked from commit 362c2f6b)

(cherry picked from commit a467c0f0)

In order to be lighter.