Improve performance of known_hosts parsing
Improve performance of known_hosts parsing

This makes two changes to known_hosts parsing:
* Only go through the work of building a regex for pattern matching if
  the entry has pattern characters (* and ?). This was ~75% performance
  improvement in the case where no patterns are being used.
* Use simple string splitting instead of a string scanner when parsing a
  single line. This was ~20% performance improvement.

Together these changes entail ~80% reduction in parsing time with no
change in behavior. In a case with a large (20k entries) known_hosts
file, the time was reduced from 350ms to 65ms.

net-ssh/net-ssh