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In particular make it work with default --with-gtest-source which is "yes".

And also set the distcheck options the same (but not completely
tested due to #1910).

(also removed an extra space out of an unrelated output)

This is incomplete and not all tested.

Added --with-gtest-source=PATH for location of the googletest source.

Also tested old method (--with-gtest not source) with gtest 1.6.0.

this should solve test failure on MacOS.  committing at my discretion.

Conflicts:
	src/lib/dns/name.cc

as suggested in #2084.  not sure why 'using namespace bind' didn't work
(and the signature is so special that there wouldn't be ambiguity)
but in any case this namespace is too large so it's better to not try to
specify the entire space.
with this change we don't need to declare using the entire space, so I
removed it, too.
okayed on jabber, directly committing.