added generic_iterator(), limit_cache() to SQLTableBase Updated SQLTable and SQLTableClustered to make full use of maxCache and arraysize valus for managing data caching and transfer from the db server. Switched to using fetchmany() for itervalues() and iteritems() iterators. Now only items() and values() methods actually force loading of the full database into cache.
added generic_iterator(), limit_cache() to SQLTableBase
Updated SQLTable and SQLTableClustered to make full use of maxCache and arraysize
valus for managing data caching and transfer from the db server.
Switched to using fetchmany() for itervalues() and iteritems() iterators.
Now only items() and values() methods actually force loading of the full
database into cache.

theoryno3/pygr,GenDataPro/pygr,theoryno3/pygr,ctb/pygr,ctb/pygr,theoryno3/pygr,cjlee112/pygr,ctb/pygr,GenDataPro/pygr,GenDataPro/pygr,cjlee112/pygr,cjlee112/pygr,RitwikGupta/pygr,ctb/pygr,RitwikGupta/pygr,RitwikGupta/pygr,ctb/pygr,cjlee112/pygr