Lint: Assigning address of auto variable 'attr' to outer scope symbol
'attrp'.

Don't leak memory on pthread_mutexattr_init or pthread_mutexattr_settype
failure.
Don't collapse errors into WT_ERROR inside __wt_cond_alloc, __wt_cond_destroy,
__wt_rwlock_alloc, return the system errors.
Merge pull request #764 from wiredtiger/mtx

Minor mutex cleanups.