BPackageInfo: Add fileName property

The property is archived and unarchived, but otherwise not yet stored.
If not set, FileName() returns CanonicalFileName(). Can be used for
packages like haiku.hpkg etc. that don't have a properly qualified file
name (yet).

headers/os/package/PackageInfo.h

@@ -70,6 +70,9 @@ public:
 			const BString&		BasePackage() const;
 			const BString&		Checksum() const;
 			const BString&		InstallPath() const;
+			BString				FileName() const;
+									// the explicitly set file name, if any, or
+									// CanonicalFileName() otherwise
 
 			uint32				Flags() const;
 
@@ -116,6 +119,7 @@ public:
 			void				SetBasePackage(const BString& basePackage);
 			void				SetChecksum(const BString& checksum);
 			void				SetInstallPath(const BString& installPath);
+			void				SetFileName(const BString& fileName);
 
 			void				SetFlags(uint32 flags);
 
@@ -299,6 +303,7 @@ private:
 
 			BString				fChecksum;
 			BString				fInstallPath;
+			BString				fFileName;
 };