Well, according to the developing done in:
  - https://git.erp5.org/gitweb/slapos.libnetworkcache.git/shortlog/refs/heads/signature?js=1

It is required to build M2Crypto, otherwise it is not possible to use
the signature feature provided by slapos.libnetworkcache.

"gzip" is undefined. Not working stuff should not be in master
branch, so revert this work.
This reverts commit dcc93a3b.

Without this, system perl will be used.

Required by maatkit.

According to commit log libpng12 section was not needed, but was refered here.