Translation of descriptions under illustrations.
Updating macports git package name

git-core has been made obsolete by the port git
[it] reviewing translation for chapter4
[it] improving translation
Remove mention of gitosis in gitolite section.

Gitosis is mentioned for no useful reason in the gitolite section.
Remove it (fixes #508).
Merge pull request #867 from daftano/it

[it] reviewing translation for chapter4
Adding homebrew as alternative to install git

It's very easy to install git with brew
Merge pull request #865 from jungkarol/master

[pl] Translation of descriptions under illustrations.
Merge pull request #866 from daftano/syncs

[it] Updating macports git package name
Merge pull request #868 from daftano/homebrew

Adding homebrew as alternative to install git
Merge pull request #869 from pepr/master

[cs] revision of chapter 4 finished
Merge pull request #870 from andrewmccarthy/issue508-gitosis

Remove mention of gitosis in gitolite section.
[cs] changes in [en] ch. 1 translated