reset is replaced with connect
PQping binding is added, but it doesn't help to detect the problem
connection.
Fixed issue #57.

Now freeChecker thread tests connection on aliveness by sending trivial
sql query (exactly 'SELECT 1;'). 

To not generate heavy trafic there is new config parameter:
aliveCheckTime in msecs that tells over which time pool should test free
connections, it is optional parameter and set by default to 3 seconds.