Redmine#1578: when creating logs, set mode to 600
Fix wrong log message when a promise is ignored due to 'ifvarclass' not matching

This situation occurs if a promise is prefixed with a "class_exp_1::" notation
and has a "ifvarclass => "class_exp_2" statement. Then the log message
says:
Skipping next promise '<promise>', as context 'class_exp_1' is not relevant
Whereas it should say:
Skipping next promise '<promise>', as var-context 'class_exp_2' is not relevant
add version comparison commands to Debian
cfengine_stdlib.cf: add package_version_equal_command and package_version_less_command to apt_get and apt_get_release bodies as well
cfengine_stdlib.cf: factor out package_version_equal_command and package_version_less_command to debian_knowledge
Merge pull request #845 from tzz/tzz/bheilman/debian_version_comparison

Add version comparison commands to Debian for all stdlib variations.
Merge pull request #828 from tzz/tzz/redmine-1578-protect-logs

Redmine#1578: when creating logs, set mode to 600
Merge pull request #840 from jooooooon/fix_log_message_about_skipping_promises_when_ifvarclass_doesnt_apply

Fix wrong log message when a promise is ignored due to 'ifvarclass' not ...