bug#18620: 25.0.50; cfengine3-make-syntax-cache

[Leo Liu]

There are multiple problems with cfengine3-make-syntax-cache:

1. call-process-shell-command changed in trunk; simply replace it with
   process-file.

2. it doesn't always return a `syntax' value

3. cf-promises doesn't have -s option in Centos 6.5 (cfengine 3.3)

HTH,
Leo