Do not require Git 2.7.3

Due to numerous vulnerabilities in previous git versions, the minimum required git version was increased from 1.7.10 to 2.7.3: 7ae573c7.

Although requiring a git version free of known security holes is commendable, requiring the latest version is probably not the best way to do so, since neither Debian 7, Debian 8 nor Ubuntu 14.04 have git 2.7.3 (or later) in their repositories. Nevertheless, all of them have fixed the recent vulnerabilities.

Debian has backported these fixes

• to git 2.1.4 for jessie (v2.1.4-2.1+deb8u2)
• to git 1.7.10.4 for wheezy (v1.7.10.4-1+wheezy3).

Ubuntu has backported these fixes to git 1.9.1 (v1.9.1-1ubuntu0.3).

Also git releases v2.6.6, v2.5.5 and v2.4.11 contain these fixes as well. So these (and higher) versions should be accepted as well.

I suggest to revert the version requirement to 1.7.10 (which is probably there for technical/feature reasons) and find another way to ensure that users don't have a vulnerable git version installed.