jdk13

[Man Alive]

Hello, I tried to install jdk13 on freshly installed 5.1-Release, but
kept encountering this error:

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===>  Building for jdk-1.3.1p8_2
# Start of jdk build
i386 Build started:   1.3.1-p8-navigator-030713-08:10
ERROR: Your BOOTDIR environment variable does not point
       to a valid Java 2 SDK for bootstrapping this build.
       A Java 2 SDK 1.3.1 build must be bootstrapped against any
       1.3 build. Please update your ALT_BOOTDIR setting, or
       just unset it, and start your build again.
                                                                                
Exiting because of the above error(s).
gmake: *** [sanity] Error 1
*** Error code 2
                                                                                
Stop in /usr/ports/java/jdk13.

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According to google, I should be installing linux-sun-jdk13 first before
trying native install (which I never did before yet installed without
problems). I tried that, successfully installed linux-sun-jdk13, but
still have problems with native installation with same error as above.
Is it possible that using linux_base-8 might be a factor (before doing
fresh install, I used linux_base (v.7) and never had problems)? Any
workarounds?

Thanks for your help and best regards, 

Jonas