Here are the installer -verboseR informations:
#> sudo installer -verboseR -allowUntrusted -dumplog -pkg JDK8u20.pkg -target /
Aug 21 18:32:19 Feline installer[97727] <Error>: IFJS: Package Authoring Error: access to path "/Library/Internet Plug-Ins/JavaAppletPlugin.plugin" requires <options allow-external-scripts='true'>
Aug 21 18:32:19 Feline installer[97727] <Error>: IFJS: Package Authoring Error: access to path "/Library/Internet Plug-Ins/JavaAppletPlugin.plugin" requires <options allow-external-scripts='true'>
Aug 21 18:32:19 Feline installer[97727] <Error>: IFJS: Package Authoring Error: access to path "/Library/Internet Plug-Ins/JavaAppletPlugin.plugin" requires <options allow external-scripts='true'>
Aug 21 18:32:19 Feline installer[97727] <Error>: IFJS: Package Authoring Error: access to path "/Library/Internet Plug-Ins/JavaAppletPlugin.plugin" requires <options allow-external-scripts='true'>
Aug 21 18:32:19 Feline installer[97727] <Error>: IFJS: Package Authoring Error: access to path "/Library/Internet Plug-Ins/JavaAppletPlugin.plugin" requires <options allow-external-scripts='true'>
Aug 21 18:32:19 Feline installer[97727] <Error>: IFJS: Package Authoring Error: access to path "/Library/Internet Plug-Ins/JavaAppletPlugin.plugin" requires <options allow-external-scripts='true'>
Aug 21 18:32:19 Feline installer[97727] <Error>: IFJS: Package Authoring Error: access to path "/Library/Internet Plug-Ins/JavaAppletPlugin.plugin" requires <options allow-external-scripts='true'>
Aug 21 18:32:19 Feline installer[97727] <Error>: IFJS: Package Authoring Error: access to path "/Library/Internet Plug-Ins/JavaAppletPlugin.plugin" requires <options allow-external-scripts='true'>
Aug 21 18:32:19 Feline installer[97727] <Error>: IFJS: Package Authoring Error: access to path "/Library/Internet Plug-Ins/JavaAppletPlugin.plugin" requires <options allow-external-scripts='true'>
Aug 21 18:32:19 Feline installer[97727] <Error>: IFJS: Package Authoring Error: access to path "/Library/Internet Plug-Ins/JavaAppletPlugin.plugin" requires <options allow-external-scripts='true'>
installer: Package name is JDK 8 Update 20
Aug 21 18:32:21 Feline installer[97727] <Debug>: Product archive /Users/cat/JDK8u20.pkg trustLevel=202
installer: Upgrading at base path /
installer:PHASE: Preparing to install...
Aug 21 18:32:22 Feline installer[97727] <Debug>: -[IFDInstallController(Private) _buildInstallPlan]: location = file://localhost
Aug 21 18:32:22 Feline installer[97727] <Debug>: -[IFDInstallController(Private) _buildInstallPlan]: file://localhost/Users/cat/JDK8u20.pkg#jdk18020.pkg
Aug 21 18:32:22 Feline installer[97727] <Debug>: -[IFDInstallController(Private) _buildInstallPlan]: file://localhost/Users/cat/JDK8u20.pkg#javaappletplugin.pkg