completion: add support for completing email aliases

Using the new --dump-aliases option from git-send-email, add completion
for --to, --cc, --bcc, and --from with the available configured aliases.

Signed-off-by: Jacob Keller <jacob.keller@gmail.com>
Signed-off-by: Jeff King <peff@peff.net>

contrib/completion/git-completion.bash

@@ -10,6 +10,7 @@
 #    *) local and remote tag names
 #    *) .git/remotes file names
 #    *) git 'subcommands'
+#    *) git email aliases for git-send-email
 #    *) tree paths within 'ref:path/to/file' expressions
 #    *) file paths within current working directory and index
 #    *) common --long-options
@@ -1711,6 +1712,15 @@ __git_send_email_suppresscc_options="author self cc bodycc sob cccmd body all"
 
 _git_send_email ()
 {
+	case "$prev" in
+	--to|--cc|--bcc|--from)
+		__gitcomp "
+		$(git --git-dir="$(__gitdir)" send-email --dump-aliases 2>/dev/null)
+		" "" ""
+		return
+		;;
+	esac
+
 	case "$cur" in
 	--confirm=*)
 		__gitcomp "
@@ -1735,6 +1745,12 @@ _git_send_email ()
 			" "" "${cur##--thread=}"
 		return
 		;;
+	--to=*|--cc=*|--bcc=*|--from=*)
+		__gitcomp "
+		$(git --git-dir="$(__gitdir)" send-email --dump-aliases 2>/dev/null)
+		" "" "${cur#--*=}"
+		return
+		;;
 	--*)
 		__gitcomp "--annotate --bcc --cc --cc-cmd --chain-reply-to
 			--compose --confirm= --dry-run --envelope-sender