copydb should not use exhaust flag when used against mongos

mongos> use foo

switched to db foo

mongos> db.bar.insert({foo: 'bar'})

WriteResult({ "nInserted" : 1 })

mongos> use admin

switched to db admin

mongos> db.runCommand({copydb: 1, fromdb: 'foo', todb: 'foo1'})

{ "ok" : 1 }

mongos> db.runCommand({copydb: 1, fromdb: 'foo', todb: 'foo2', fromhost: 'localhost:27017'})

{

	"errmsg" : "exception: nextSafe(): { $err: \"the 'exhaust' query option is invalid for mongos queries: foo.bar { query: {}, $snapshot: true }\", code: 18526 }",

	"code" : 13106,

	"ok" : 0

}

mongos> db.runCommand('buildInfo')

{

	"version" : "2.7.7-pre-",

	"gitVersion" : "ccacca83853931e2d03c8670c1745dfac515e119 modules: subscription",

	"OpenSSLVersion" : "OpenSSL 1.0.1i 6 Aug 2014",

	"sysInfo" : "Linux devbox 3.16.1-gentoo #1 SMP PREEMPT Thu Aug 14 08:35:28 PDT 2014 x86_64 BOOST_LIB_VERSION=1_49",

	"loaderFlags" : "-fPIC -pthread -Wl,-z,now -rdynamic -Wl,-E",

	"compilerFlags" : "-Wnon-virtual-dtor -Woverloaded-virtual -std=c++11 -fPIC -fno-strict-aliasing -ggdb -pthread -Wall -Wsign-compare -Wno-unknown-pragmas -Winvalid-pch -pipe -Werror -O3 -Wno-unused-local-typedefs -Wno-unused-function -Wno-deprecated-declarations -Wno-unused-but-set-variable -fno-builtin-memcmp -std=c99",

	"allocator" : "tcmalloc",

	"versionArray" : [

		2,

		7,

		7,

		-100

	],

	"javascriptEngine" : "V8",

	"bits" : 64,

	"debug" : false,

	"maxBsonObjectSize" : 16777216,

	"ok" : 1

}