Added MSV1_0_ALLOW_MSVCHAPV2 flag to ntlm_auth

[github at samba.org]

New comment by qnet-herwin on Samba Github repository

https://github.com/samba-team/samba/pull/45#issuecomment-163700340
Comment:
I've added a comparable patch to FreeRADIUS (see https://github.com/FreeRADIUS/freeradius-server/commit/37f2f6d8e09bdebdf3031e419c00a0d3193b074a), where it arose the question if this flag shouldn't be enabled as default. The original commit on the mailing lists added is as default instead of an option, and the flags `MSV1_0_ALLOW_WORKSTATION_TRUST_ACCOUNT` and `MSV1_0_ALLOW_SERVER_TRUST_ACCOUNT` are hardcoded in the source as well.

It is a behavioural change, and I honestly have no idea if this could break anything. Hardcoding the flag would definitely result in cleaner code.