Bug in to_tsquery(), and fix

A customer reported a mysterious crash, with the backtrace showing it to 
come from several levels down deep in the infix() function, called by 
tsqueryout(). I was eventually able to reproduce this and hunt down the 
bug, using the same tsquery string as the customer.

The bug was actually in to_tsquery(), and resulted in a corrupt 
"operand" string being stored in a tsquery Datum. In a nutshell, in 
to_tsquery_byid(), we're using memcpy() to copy to a possibly 
overlapping region of data. The obvious fix is to use memmove() instead, 
attached.

This is pretty hairy code, it's hard to resist doing some more whacking 
around. For example the infix() function would be a lot simpler if it 
used a StringInfo instead of implementing a resizeable string of its 
own. But I'll leave that alone for now, given that the bug was in fact 
not in that function.

-- 
   Heikki Linnakangas
   EnterpriseDB   http://www.enterprisedb.com