gcc_release (announce_snapshot): Add substitution of @BRANCH for README and index...

gcc_release (announce_snapshot): Add substitution of @BRANCH for README and index.html.

	* gcc_release (announce_snapshot): Add substitution of @BRANCH
	for README and index.html.  Remove substitution of @LONG_DATE.
	Put index.html into the respective snapshot directory.
	Adjust subject of the notification mail to the new naming scheme
	for CVS tags.
	Adjust name of the LATEST-IS-... files to the new naming scheme
	for snapshot directories.
	(FTP_PATH): Ditto.
	(LAST_DIR): Ditto.
	(LAST_LONG_DATE): Remove.

	* snapshot-README: Adjust to the new naming schemes for directories
	and snapshots per se.
	Dynamically fill in the respective branch instead of hardcoding it.

	* snapshot-index.html: Replace individual links to diffs with a
	general link to the diff/ subdirectory.
	Mention the concrete snapshot in <title> and <h1>.
	Adjust links to the new location of index.html.

From-SVN: r69143