Simplify CMutexLock

[alexanderkjeldaas]

o Remove unused Leave and GetLock functions
o Make Enter and TryEnter private.
o Simplify Enter and TryEnter.
boost::unique_lock doesn't really know whether the
mutex it wraps is locked or not when the defer_lock
option is used.
The boost::recursive_mutex does not expose this
information, so unique_lock only infers this
knowledge. When taking the lock is defered, it
(randomly) assumes that the lock is not taken.
boost::unique_lock has the following definition:

    unique_lock(Mutex& m_,defer_lock_t):
        m(&m_),is_locked(false)
    {}

    bool owns_lock() const
    {
        return is_locked;
    }

Thus it is a mistake to check owns_lock() in Enter
and TryEnter - they will always return false.

[sipa]

ACK on the code changes, but one nitpick: can you separate the git commit summary (the first line) and the rest? Some git tools assume everything up to the first empty line is the summary.

[alexanderkjeldaas]

Done.

[sipa]

ACK

[Diapolo]

Compiles just fine on Windows and causes no obvious problems, can't really comment on the changes though.

[BitcoinPullTester]

Automatic sanity-testing: PASSED, see http://jenkins.bluematt.me/pull-tester/bfc96207998c284e2cb6eb99c99b755a161e723d for binaries and test log.