driver settings: Remove dead load_driver_settings_from_path()

load_driver_settings() supports being passed an absolute path.
driver settings: Add load_driver_settings_file()

Allows loading an already opened driver settings file (by FD).
khash: Move string hash functions to own header/source file

Unlike khash they shouldn't be phased out (only renamed).
packagefs: Support blacklisting entries in packages

In each installation location, it is now possible to create a settings
file "packages" that allows to blacklist entries contained in packages.
The format is:

Package <package name> {
	EntryBlacklist {
		<entry path>
		...
	}
}
...

<package name> is the base name (no version) of the respective package
(e.g. "haiku"), <entry path> is an installation location relative path
(e.g. "add-ons/Translators/FooTranslator").

Blacklisted entries will be ignored by packagefs, i.e. they won't appear
in the file system. This addresses the issue that it may be necessary to
remove a problematic file (e.g. driver, add-on, or library), which would
otherwise require editing the containing package file.

The settings file is not not "live". Changes take effect only after
reboot (respectively when remounting the concerned packagefs volume).