Make git apply working in non-root-git directories

[mvorisek]

git is the right choise for appliing patches as it is available more than every other solution at the most dev/prod systems, espetially non-linux ones like Windows, where the patch alternative is not often installed (or at least it is not available from the PATH).

I have analysed the issue related with issue #148 ( https://stackoverflow.com/questions/24821431/git-apply-patch-fails-silently-no-errors-but-nothing-happens/#27283285 ):

Problem:
patch is not applied via git apply if outside .git directory, in this case Skipped patch '<file path>'. verbose warning is show.

Analysis:

1. trigerred here: https://github.com/git/git/blob/b02fd2accad4d48078671adf38fe5b5976d77304/apply.c#L4696
2. based on condition https://github.com/git/git/blob/b02fd2accad4d48078671adf38fe5b5976d77304/apply.c#L4681
3. the condition is not matched in case of not matching state->prefix (.git directory root path) https://github.com/git/git/blob/b02fd2accad4d48078671adf38fe5b5976d77304/apply.c#L2077
4. state->prefix is set solely here https://github.com/git/git/blob/b02fd2accad4d48078671adf38fe5b5976d77304/apply.c#L93
5. from setup_git_directory_gently() https://github.com/git/git/blob/99c33bed562b41de6ce9bd3fd561303d39645048/git.c#L416 line as the git apply command is marked with RUN_SETUP_GENTLY option
6. setup_git_directory_gently() function tries to find .git directory and then it tests it with is_git_directory https://github.com/git/git/blob/bc12974a897308fd3254cf0cc90319078fe45eea/setup.c#L311 , this function tests the presence of these files:
   • .git/objects/
   • .git/refs/
   • .git/HEAD

These files needs to be presented in order to make git patch working.

PR submitted.

[cweagans]

See #296 (comment)