Update gxemul to 0.6.0. Okay'ed by wiz@, in PR pkg/43296 by me.

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The main change between release 0.4.7.2 and 0.6.0 is:

 * Since late 2007, a complete rewrite of the emulator's base framework
   has been going on. GXemul 0.6.0 is a very early release of the new
   framework. So far, only the testm88k machine mode has been rewritten
   to use the new framework, all other machine modes run in legacy mode
   using the old framework (which is still included).

   In other words: For most emulation modes, 0.6.0 will be exactly
   like 0.4.7.2.

 In addition to the new framework, a couple of other changes are
 worth mentioning:

 * Many unused, rarely used, and bogus emulation modes and features
   were removed, to reduce the maintenance burden.

 * Some operating systems listed on the guest OS page have had
   new releases; the documentation has been updated to reflect this.

 * New source code (but not the legacy part) is documented using
   Doxygen comments, and there is a unit testing framework in place.

 * There is now finally an install Makefile target, and the -j make
   option can be used to parallelize builds.

Please read the HISTORY file for more details.
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Also update pkgsrc files:
 * update COMMENT and DESCR per the latest release note
 * remove MAKE_JOBS_SAFE=no as mentioned in the above changes list.


(tsutsui)