Support extracting archives to the packages we build

* BuildHaikuPackage rule: Create the script that contains the extraction
  commands.
* build_haiku_package: Add extractFile() function (stripped down version
  from build_haiku_image).

In build_haiku_image the functionality was mainly used to extract the
optional packages, which is no longer done. We still need it e.g. for
the Wifi firmware packages that want to be extracted.

build/jam/PackageRules

@@ -334,14 +334,16 @@ rule BuildHaikuPackage package : packageInfo
 	# create the other scripts
 	local makeDirsScript = <$(grist)>haiku.package-make-dirs ;
 	local copyFilesScript = <$(grist)>haiku.package-copy-files ;
+	local extractFilesScript = <$(grist)>haiku.package-extract-files ;
 
 	MakeLocate $(makeDirsScript) $(copyFilesScript) : $(scriptDir) ;
 
 	CreateContainerMakeDirectoriesScript $(package) : $(makeDirsScript) ;
 	CreateContainerCopyFilesScript $(package) : $(copyFilesScript) ;
+	CreateContainerExtractFilesScript $(package) : $(extractFilesScript) ;
 
 	local scripts = $(initVariablesScript) $(makeDirsScript)
-		$(copyFilesScript) ;
+		$(copyFilesScript) $(extractFilesScript) ;
 
 	# call the build actions
 	local mainScript = build_haiku_package ;