fix error message for older Git versions
git branch gave a different error message before version 1.5.4.rc0
before 1.7.0.rc0 git status would exit 1 in a dirty work tree

switch to testing with 'git version', which always exits 0
git clone on an empty repository dies for git between 1.7.0.rc1 and 1.7.0.2
skip some git submodule failures

git submodule add with a non-existing path fails
for git between 1.7.0.rc1 and 1.7.0.2
remove a useless test that fails with git < 1.5.1.rc1

git --pretty:format=%s is not supported until git 1.5.1.rc1
remove the now useless output test
skip some more git submodule failures

git submodule add with a non-existing path fails
for all subversions of git 1.5.4 and git 1.5.5
git init is actually available since git 1.5.0.rc1
also test with the release candidates for git 1.5.0 when possible

test_repository (from Test::Git) actually works with at least git 1.5.0.rc1

when that function is not used, move the required version
as far as 1.5.0.rc0 when possible
create a repository with a commit pointing to a non-empty tree
git clone with local repositories fails for git between 1.5.4.rc0 and 1.6.0.rc0
Merge branch 'vintage-git'
silence a warning ("Already on 'master'") in recent versions of git
Changes for version 1.304