Fix random_device to work with COW strings again

Fix random_device to work with COW strings again

Instead of duplicating the initialization functions that take string,
add a new member taking a raw pointer that can be used to convert the
constructor token from the old string to the new.

Also fix "mt19337" typos in a testcase.

	* include/bits/random.h (random_device::_M_init(const char*, size_t)):
	Add new private member function.
	* src/c++11/cow-string-inst.cc (random_device::_M_init(const string&))
	(random_device::_M_init_pretr1(const string&)): Call new private
	member with string data.
	* src/c++11/random.cc (random_device::_M_init(const char*, size_t)):
	Define.
	* testsuite/26_numerics/random/random_device/cons/default-cow.cc: New
	test using COW strings.
	* testsuite/26_numerics/random/random_device/cons/default.cc: Generate
	a value from the device.
	* testsuite/26_numerics/random/random_device/cons/token.cc: Likewise.
	Fix typo in token string.

From-SVN: r271805