pg_hba.conf.sample wording improvement

I propose the attached patch to shake up the wording in the connection 
type section of pg_hba.conf.sample a bit.  After the hostgssenc part was 
added on, the whole thing became a bit wordy, and it's also a bit 
inaccurate for example in that the current wording for "host" appears to 
say that it does not apply to GSS-encrypted connections.