/restful/meshms/SID/SID/sendmessage now enforces Content-Disposition:
form-data (was ignoring), and enforces Content-Type: text/plain;
charset=utf-8 (was ignoring)
New negative test cases to ensure that these are treated strictly
Introduce "enum meshms_status" to replace int -1,0,1 for return values
from MeshMS internal functions
Add test cases to check that status 2 is returned when attempting to
send a message from an identity that is not known (unlocked)
