on current jruby-1_7 branch
$ bin/jruby -Xnative.verbose=true -I"lib" --1.9 -I test/externals/ruby1.9 -I test/externals/ruby1.9/ruby -r ./test/ruby19_env.rb -r minitest/excludes "test/externals/ruby1.9/ruby/test_m17n_comb.rb"
Successfully loaded native POSIX impl.
Run options:

Running tests:

................E..............................

Finished tests in 8.964000s, 5.2432 tests/s, 8112.0036 assertions/s.

1. Error:
   test_str_crypt(TestM17NComb):
   Java::JavaLang::NullPointerException:
   org.jruby.RubyString.crypt(RubyString.java:2660)
   org.jruby.RubyString$INVOKER$i$1$0$crypt.call(RubyString$INVOKER$i$1$0$crypt.gen)
   org.jruby.runtime.callsite.CachingCallSite.cacheAndCall(CachingCallSite.java:326)
   org.jruby.runtime.callsite.CachingCallSite.call(CachingCallSite.java:170)
   test.externals.ruby1_dot_9.ruby.test_m17n_comb.block_82$RUBY$test_str_crypt(test/externals/ruby1.9/ruby/test_m17n_comb.rb:795)
   test$externals$ruby1_dot_9$ruby$test_m17n_comb$block_82$RUBY$test_str_crypt.call(test$externals$ruby1_dot_9$ruby$test_m17n_comb$block_82$RUBY$test_str_crypt)
   org.jruby.runtime.CompiledBlock19.yield(CompiledBlock19.java:135)
   org.jruby.runtime.CompiledBlock19.yieldSpecific(CompiledBlock19.java:97)
   org.jruby.runtime.Block.yieldSpecific(Block.java:120)
   org.jruby.ast.YieldOneNode.interpret(YieldOneNode.java:35)