/lib/libz.so version bump prevents java/jdk1* from upgrading

[Alexander Best]

hi there,

it would be nice to have a note in UPDATING on how to rebuild an installed
java/jdk1* under >= 8. since java/jdk1* requires an installed java environment
in order to build it fails due to the version bump of /lib/libz.so.4 to
/lib/libz.so.5

to be able to rebuild any installed java/jdk1* one needs to install
misc/compat7x. after installation of java/jdk1* finishes misc/compat7x can
safely be deleted (if it's not required by any other port).

i haven't checked what the situation is like when no java environment is
installed, but i believe this doesn't cause a problem since java/diablo-jdk*
is used for bootrapping then.

cheers.
alex