Create post-commit git hook to send commit emails

Commit notification e-mail

--------------------------

To configure commit notification e-mails for the first time, do the following:

- the following should be done regardless commit notification:

  = install git;

  = run git config --global user.name "<Your Name>"

  = run git config --global user.email "<your email>"

- clone/pull this tree (further it's location is <this tree>);

- create a folder <git templates>;

- symlink <this tree>/git_template/hooks to <git templates path>/hooks;

- configure git templates location globally:

  = for git versions >= 1.7.1, run 

    git config --global init.templatedir <git templates path>

  = for older git versions, set the environmemnt variable 

    GIT_TEMPLATE_DIR=<git templates path> 

    and make sure it is always set whenever you work with git;

- run git config --global hooks.postcommitrecipients "<comma-separated list of addresses to send emails to>;

- run git config --global hooks.postcommitbranches "<space-separated list of branches> (* wildcard is allowed)

- optionally:

  = run git config --global hooks.postcommitsender <e-mail to send notifications from> 

  = run git config --global hooks.postcommitmailer <path to mailer> 

    if anything other than /usr/sbin/sendmail is to be used

- make sure <this tree>/git_template/hooks/post-commit-email is executable;

Example (most common set of commands):

bzr branch lp:mariadb-tools 

mkdir $HOME/.git_template/

ln -s `pwd`/mariadb-tools/git_template/hooks $HOME/.git_template/hooks

git config --global init.templatedir $HOME/.git_template

git config --global hooks.postcommitrecipients "commits@mariadb.org"

git config --global hooks.postcommitbranches "*"

From now on, for all new clones of branches listed in hooks/postcommitbranches, 

commit notifications should be sent. 

If you had already cloned some trees before enabling commit notifications, 

you will need to amend those trees:

cd <cloned folder>

rm -rf .git/hooks

ln -s <this tree>/git_template/hooks .git/hooks

To disable commit notification(s), set SKIP_COMMIT_EMAIL environment variable 

to a non-empty value or set hooks.postcommitbranches to an empty value.

Notes:

- hooks/postcommitrecipients is a *comma-separated* list of e-mails. Normally, 

  it is expected to contain the commit mailing list, but you can add some other

  address(es) or change it if you wish;

- hooks/postcommitbranches is a *space-separated* list of branches affected 

  by the post-commit hook. Asterisk wildcard is allowed. 

  Please note that these are *real* git branches, as opposed to branch nicknames. 

Examples:

Assuming you did the following

  git clone https://github.com/MariaDB/server 10.1-mdev1234

  ...

  git branch

  # * 10.1

  git commit -a

 Example 1:

  postcommitbranches = 10.0 10.1 10.2

  # The commit e-mail will be sent because the current branch is 10.1, 

  # it's on the list

  Example 2:

  postcommitbranches = 10.0-* 10.1-* 10.2-*

  # The commit e-mail won't be sent because the current branch is 10.1, 

  # it does not match the pattern 10.1-*

  Example 3:

  postcommitbranches = 10*

  # The commit e-mail will be sent