Switch package file accessor classes to use BPositionIO

* PackageFileHeap{Reader,Writer} as well as Package{Reader,Writer} and
  their implementation and super classes do now internally use a
  BPositionIO instead of a FD to access the package file. This provides
  more flexibility needed for features to come.
* BPackageReader has already grown a new Init() version with a
  BPositionIO* parameter.

headers/os/package/hpkg/PackageReader.h

@@ -9,6 +9,9 @@
 #include <SupportDefs.h>
 
 
+class BPositionIO;
+
+
 namespace BPackageKit {
 
 namespace BHPKG {
@@ -34,12 +37,14 @@ public:
 
 			status_t			Init(const char* fileName, uint32 flags = 0);
 			status_t			Init(int fd, bool keepFD, uint32 flags = 0);
+			status_t			Init(BPositionIO* file, bool keepFile,
+									uint32 flags = 0);
 			status_t			ParseContent(
 									BPackageContentHandler* contentHandler);
 			status_t			ParseContent(BLowLevelPackageContentHandler*
 										contentHandler);
 
-			int					PackageFileFD();
+			BPositionIO*		PackageFile() const;
 
 			BAbstractBufferedDataReader* HeapReader() const;
 									// Only valid as long as the reader lives.