Added new optional option mailsubject to body executor control, default [hostname/ip] + unit test
cf-execd: send X-CFEngine SMTP header if mailsubject set
Merge branch 'dev/mailsubject/xcfengine-header2' of https://github.com/cdituri/core

Conflicts:
	cf-execd/cf-execd-runner.c
	tests/unit/data/body_executor_control_full.cf
Use safe string functions and silence a warning.