c++11: fix std::lock naming conflicts

c++11: fix std::lock naming conflicts

Unfortunately, 'using namespace std;' is in pretty widespread use in the Ceph
tree, so we need to rename to avoid the conflict.

Example error output:

test/streamtest.cc:37:19: error: reference to 'lock' is ambiguous
  Mutex::Locker l(lock);
                  ^
test/streamtest.cc:32:7: note: candidate found by name lookup is 'lock'
Mutex lock("streamtest.cc lock");
      ^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/mutex:346:1: note: candidate found by name lookup is 'std::__1::lock'
lock(_L0& __l0, _L1& __l1)

Signed-off-by: Noah Watkins <noahwatkins@gmail.com>