This teaches pytype about some lazy initialization, and avoids the following:
File "/mnt/c/Users/Matt/hg/mercurial/chgserver.py", line 666, in _checkextensions: No attribute '_hashstate' on chgunixservicehandler [attribute-error] File "/mnt/c/Users/Matt/hg/mercurial/chgserver.py", line 672, in _checkextensions: No attribute '_hashstate' on chgunixservicehandler [attribute-error] File "/mnt/c/Users/Matt/hg/mercurial/chgserver.py", line 677, in _bind: No attribute '_realaddress' on chgunixservicehandler [attribute-error] File "/mnt/c/Users/Matt/hg/mercurial/chgserver.py", line 683, in _bind: No attribute '_realaddress' on chgunixservicehandler [attribute-error] File "/mnt/c/Users/Matt/hg/mercurial/chgserver.py", line 686, in _createsymlink: No attribute '_baseaddress' on chgunixservicehandler [attribute-error] File "/mnt/c/Users/Matt/hg/mercurial/chgserver.py", line 686, in _createsymlink: No attribute '_realaddress' on chgunixservicehandler [attribute-error] File "/mnt/c/Users/Matt/hg/mercurial/chgserver.py", line 688, in _createsymlink: No attribute '_baseaddress' on chgunixservicehandler [attribute-error] File "/mnt/c/Users/Matt/hg/mercurial/chgserver.py", line 689, in _createsymlink: No attribute '_realaddress' on chgunixservicehandler [attribute-error] File "/mnt/c/Users/Matt/hg/mercurial/chgserver.py", line 690, in _createsymlink: No attribute '_baseaddress' on chgunixservicehandler [attribute-error]