The posix driver was developed over time and the naming is not very consistent.
Rename the files and functions to work well with other drivers and generally favor longer names since the driver functions are seldom (eventually never) used outside the driver itself.
* Add storageCopy(), storageMove(), and storagePathSync().
* Separate StorageFile object into separate read and write objects.
* Abstract out Posix file read/write objects.
Mainly this helps with unit tests that need to do log expect testing. Add harnessCfgLoad() test function, which allows a new config to be loaded for unit testing without resetting log functions, opening a log file, or taking locks.
Now only two types of locks can be taken: archive and backup. Most commands use one or the other but the stanza-* commands acquire both locks. This provides better protection than the old command-based locking scheme.
This implementation should be faster because it does not stat each file. It simply assumes that most directory entries are files so attempts an unlink() first. If the entry is reported by error codes to be a directory then it attempts an rmdir().
This option allows pgBackRest to validate page checksums in data files when checksums are enabled on PostgreSQL >= 9.3. Note that this functionality requires a C library which may not initially be available in OS packages. The option will automatically be enabled when the library is present and checksums are enabled on the cluster.
