Changing log level for file diff, it isn't critical
Don't allow npm state to be used if npm module not available

This prevents a traceback (as seen in #5934) when one tries to run an
npm state when the npm module is not available, by preventing the npm
state from loading using the __virtual__() function.
Add test to see if specified gid is free

The errormessage uf you specified a GID that was already taken was not really helping for debugging, and the lack of this test caused logentries ('groupadd' was called anyway, which errored).
fix doc hyperlink
img module: bugfix for mount_image
fix 2-space indents in states/group.py
fix name of 1st param of SaltLoggingClass.__new__()

************* Module salt.log
C0202:142,4:SaltLoggingClass.__new__: Class method __new__ should have 'cls' as first argument
fix spelling: dependancy ==> dependency
Depends.enforce_dependencies: self => cls, since it's a classmethod
OutputOptionsWithTextMixIn.__new__(): wrong class in super() call

************* Module salt.utils.parsers
E1003:854,4:OutputOptionsWithTextMixIn.__new__: Bad first argument 'OutputOptionsMixIn' given to super class
call dict.__init__() in OrderedDict.__init__()

************* Module salt.utils.odict
W0231: 50,12:OrderedDict.__init__: __init__ method from base class 'dict' is not called
pylint pragmas: `enable-msg` is deprecated, replace it with `enable`

fixes pylint runtime "DeprecationWarning: enable-msg is deprecated, replace it with enable" messages
changed publish_sesion to publish_session into master
Let's make `SaltLoggingClass` a new style class. Fixes #5989.
Create a NO-OP mixin to shut up pylint. Fixes #5989.

Craeted a simple new style class to make pylint shut up, because SaltLoggingClass can't subclass `object` directly:

     'Cannot create a consistent method resolution order (MRO) for bases'
spelling: dependant ==> dependent
fix documentation to match function name saltutil.revoke_auth
one underscore is sufficient: __NewStyleClassMixIn => _NewStyleClassMixIn
Fix metaclass __new__() parameter naming: cls ==> mcs

************* Module salt.utils.parsers
C0204: 43,4:MixInMeta.__new__: Metaclass class method __new__ should have 'mcs' as first argument
C0204: 54,4:OptionParserMeta.__new__: Metaclass class method __new__ should have 'mcs' as first argument
salt/utils/yamlloader.py: fix typos in comments