Add BLowLevelPackageContentHandler section hooks

* Add hooks HandleSectionStart() and HandleSectionEnd(). They are
  invoked to bracket package file section, so the handler can
  discriminate which section the attributes belong to.
  HandleSectionStart() features a return parameter _handleSection, which
  allows to handler to pick which sections it wants to handle.
* "package dump" does now print the section names.

headers/os/package/hpkg/PackageContentHandler.h

@@ -26,6 +26,12 @@ class BLowLevelPackageContentHandler {
 public:
 	virtual						~BLowLevelPackageContentHandler();
 
+	virtual	status_t			HandleSectionStart(
+									BHPKGPackageSectionID sectionID,
+									bool& _handleSection) = 0;
+	virtual	status_t			HandleSectionEnd(
+									BHPKGPackageSectionID sectionID) = 0;
+
 	virtual	status_t			HandleAttribute(BHPKGAttributeID attributeID,
 									const BPackageAttributeValue& value,
 									void* parentToken, void*& _token) = 0;

headers/private/package/hpkg/ReaderImplBase.h

@@ -51,11 +51,15 @@ protected:
 				uint64			heapOffset;
 				uint64			heapSize;
 
-				AttributeHandlerContext(BErrorOutput* errorOutput,
-					BPackageContentHandler* packageContentHandler);
+				BHPKGPackageSectionID	section;
 
 				AttributeHandlerContext(BErrorOutput* errorOutput,
-					BLowLevelPackageContentHandler* lowLevelHandler);
+					BPackageContentHandler* packageContentHandler,
+					BHPKGPackageSectionID section);
+
+				AttributeHandlerContext(BErrorOutput* errorOutput,
+					BLowLevelPackageContentHandler* lowLevelHandler,
+					BHPKGPackageSectionID section);
 
 				void ErrorOccurred();
 			};
@@ -200,7 +204,8 @@ protected:
 									AttributeHandlerContext* context,
 									AttributeHandler* rootAttributeHandler);
 			status_t			ParseAttributeTree(
-									AttributeHandlerContext* context);
+									AttributeHandlerContext* context,
+									bool& _sectionHandled);
 
 	virtual	status_t			ReadAttributeValue(uint8 type, uint8 encoding,
 									AttributeValue& _value);
@@ -225,6 +230,9 @@ protected:
 			SectionInfo			fPackageAttributesSection;
 
 private:
+			status_t			_ParseAttributeTree(
+									AttributeHandlerContext* context);
+
 	template<typename Type>
 	inline	status_t			_Read(Type& _value);