Support reading GIT_AUTHOR_{NAME,EMAIL} env variables

Change the discovery of the user.name and user.email variables to
first look up the user/name in the GIT_AUTHOR_NAME and
GIT_AUTHOR_EMAIL environment variables. This mirrors the behavior of
Git itself, see git-commit-tree(1) for details.

The reason to do this is that managing your Git identity via these
variables can be more conveniente than setting them in a config file,
it makes it easier to set them differently on different hosts.

Also change the error message we display if these aren't set, we'll
now error out with something like this when we can't get an author
name or an E-Mail;

    $ perl -Ilib bin/git-deploy start
    # FATAL: Please make sure you set your Git user name & E-Mail
    # FATAL: before using this tool, i.e. either run:
    # FATAL:
    # FATAL:     git config --global user.name 'Your Name'
    # FATAL:     git config --global user.email 'email@host.com'
    # FATAL:
    # FATAL: Or make sure the GIT_AUTHOR_NAME and GIT_AUTHOR_EMAIL
    # FATAL: environment variables are appropriately set.

This patch is inspired by Rob's
#20, I thought it made
more sense to introduce a function for looking up the user name &
E-Mail rather than hooking into the low-level config mechanism. This
also adjusts our documentation to indicate to users that they can use
this instead of setting user.{name,email}.

bin/git-deploy

@@ -74,8 +74,8 @@ sub send_email_with_sendmail {
 
     my $handle;
     my $sendmail= get_config("mail-tool","/usr/sbin/sendmail -f");
-    my $from_name= get_config("user.name");
-    my $from_email= get_config("user.email");
+    my $from_name= get_user_name();
+    my $from_email= get_user_email();
 
     my $cmd= "$sendmail '$from_email' '$to_mail'";
     if ( $to_mail eq 'debug' ) {
@@ -641,12 +641,14 @@ if ( $list || $show_tag ) {
     exit(0);
 }
 
-if (!$force and (!get_config("user.name","") or !get_config("user.email",""))) {
-    _die  "Please make sure you execute:\n\n"
+if (!$force and (!get_user_name() or !get_user_email())) {
+    _die  "Please make sure you set your Git user name & E-Mail\n"
+        . "before using this tool, i.e. either run:\n\n"
         . "    git config --global user.name 'Your Name'\n"
         . "    git config --global user.email 'email\@host.com'\n"
         . "\n"
-        . "before you use this tool";
+        . "Or make sure the GIT_AUTHOR_NAME and GIT_AUTHOR_EMAIL\n"
+        . "environment variables are appropriately set.";
 }
 
 if ($check_clean) {
@@ -1637,8 +1639,14 @@ L<git-config(1)> for details:
 
 =item * user.name
 
+You can also make sure C<GIT_AUTHOR_NAME> is set. See
+L<git-commit-tree(1)> for details.
+
 =item * user.email
 
+You can also make sure C<GIT_AUTHOR_EMAIL> is set. See
+L<git-commit-tree(1)> for details.
+
 =back
 
 And these are L<git-deploy(1)>-specific options:

lib/Git/Deploy.pm

@@ -39,6 +39,8 @@ our @EXPORT= qw(
     get_config_int
     get_config_path
     get_config_bool
+    get_user_name
+    get_user_email
     get_current_branch
     get_deploy_file_name
     get_ref_info
@@ -247,6 +249,9 @@ sub get_config_path { return _get_config("--path",@_) }
 sub get_config_int  { return _get_config("--int",@_) }
 sub get_config_bool { return 'true' eq _get_config("--bool",@_) } 
 
+sub get_user_name  { return $ENV{GIT_AUTHOR_NAME}  || get_config("user.name", "") }
+sub get_user_email { return $ENV{GIT_AUTHOR_EMAIL} || get_config("user.email", "") }
+
 }