added I2C device check

git-svn-id: svn://svn.code.sf.net/p/fhem/code@5345 2b470e98-0d58-463d-a4d8-8e2adae1ed80
commandref modified

git-svn-id: svn://svn.code.sf.net/p/fhem/code@5346 2b470e98-0d58-463d-a4d8-8e2adae1ed80
added support for physical i2c device modules

git-svn-id: svn://svn.code.sf.net/p/fhem/code@5347 2b470e98-0d58-463d-a4d8-8e2adae1ed80