Install git instead of git-core with yum

The repository of yum seems that may be installed git instead of
git-core as same as the Debian based distributions.
Merge pull request #851 from okuryu/yum-git

Install git instead of git-core with yum
[it] updating chapter 1

Così suona meglio
Updating yum package name for git

Currently seems the repository of yum has a git package instead of git-core. Now it's the same as for Debian based distributions.

See also PR #851
change past tense to present in commit msgs in chapter 3.2 (Branching)
Merge pull request #852 from daftano/master

[it] Updating chapter 1 with PR#851d changes
Merge pull request #853 from daftano/chapter1

[it] updating chapter 1
Merge pull request #854 from petervojtek/change_past_tense_to_present_in_commit_msgs_in_chapter_3_2_branching

Change past tense to present in commit msgs in chapter 3.2 (Branching)
Merge branch 'progit/master' into ja