Report error if messages sent to plm are of an incorrect length

- Add sub insteon_cmd_len to Message_Decoder. Returns expected byte length
- Add error message if command sent to plm is improper length

* After testing need to add coding to skip sending an incorrect message

Start of fix for Hollie/misterhouse#83
Clear messages sent to PLM if of incorrect length
Remove no_hop_increase flag from NACK logic

Messages that are NACKed are dropped not resent.  So there is no concern that a hop_increase will be recorded.
POD added to ~_Items.pm
faq.pod update by Vargester requested by Stovenour
Enable DTR on the serial port when checking for new data from an MR26, as a CM17 on the same port may switch it off
Add a comment explaining why the DTR signal may need to be activated again
Merge pull request #106 from c99koder/MR26_FIX

Enable DTR on the serial port when checking for new data from an MR26
Merge pull request #105 from drobinson0919/master

POD added to ~_Items.pm
Merge pull request #100 from krkeegan/fix_issue_83

Drop Bad Messages Sent to PLM
Merge pull request #101 from krkeegan/hop_tracking

Remove no_hop_increase flag from NACK logic
Fix Issue #104:  Add Objects, Items, and Modules links to TOC