Generic LinkedList implementation.

Data agnostic linked list using reference counting to provide both
implicit sharing and copy on write.
Merge pull request #289 from cduclos/master

Generic linked list implementation
Style corrections for new list, refcount
Move statistics to libutils
Take out some more misplaced FatalErrors, reduce reliable on eval state
Unexport CopyFileSources
Unexport FSWrite
Unexport DeleteHash
Unexport NewHashValue
Unexport SourceSearchAndCopy
Unexport VerifyCopy
Unexport CopyRegularFile
Unexport LinkCopy
Move files_links.h to cf-agent (Redmine #1973)
Remove unused function
chmod -x on source code
Move files promise type-related functions from libpromises (Redmine #1973)
Add missing include
Fix errorneous CF_SAME_GROUP used as uid_t. Silences warning on OS X
Fix ExecSanityChecks to properly set up default value of umask