fix matching a IPv6 address as host

When the host is something like '[::1]' or '[::1]:8080',
_get_host_handlers gets wrong hosts string.
Merge branch 'master' into fix-ipv6-host
remove executable permission from tornado.web
move code to seperate function 'split_host_and_port'
Merge pull request #1261 from lilydjwg/fix-ipv6-host

fix matching an IPv6 address as host