Using platform.h instead of system headers

This way all the logic for deciding which headers need to be called is
kept inside platform.h.
Merge pull request #675 from cduclos/master

platform.h instead of system headers for HPUX
Set of fixes to logging.
  - Fix setting debug level in options.
  - General standardization of logging
Moar changes
Bring master ChangeLog up to speed wrt 3.4 fixes
Fix MinGW build for output review
Add function categories

This is for output in cf-promises --syntax-description for automatic categorization
of functions for documentation.
Rename ScopeDeleteSpecialScalar -> ScopeDeleteSpecial
Remove ScopeNewScalar, convert to EvalContextVariablePut
Remove ScopeNewList, convert to EvalContextVariablePut
Combine ScopeNewSpecialScalar, ScopeNewSpecialList -> ScopeNewSpecial
cannot create documentation for cfengine stdlib with those two misplaced parenthesis
Merge pull request #678 from jimis/master

Changelog update.
Merge pull request #680 from jremond/parenthesis_misplaced

cfengine_stdlib typo breaks documentation generation
More ChangeLog entries.
Merge pull request #685 from kacfengine/changelog

More ChangeLog entries.
fixing a mem leak. Never free what you insert in a StringMap
Merge pull request #686 from jeffali/fix/memleak1

fixing a mem leak. Never free what you insert in a StringMap unless you xstrdup it.