Added Y2DISABLELANGUAGEPLUGINS (gh##20)

Enabled ignoring language bindings (yast2-ruby-bindings,
yast2-perl-bindings, yast2-python-bindings) by setting the
environment variable Y2DISABLELANGUAGEPLUGINS.

liby2/src/Y2LanguageLoader.cc

@@ -57,6 +57,12 @@ THis does not work because the environment may be already destroyed
 
 Y2LanguageLoader::Y2LanguageLoader ()
 {
+    if (getenv ("Y2DISABLELANGUAGEPLUGINS"))
+    {
+        // https://github.com/yast/yast-core/issues/20
+        return;
+    }
+
     glob_t glob_buf;
     int glob_flags = 0;
     if (YCPPathSearch::numberOfComponentLevels() == 0)

libycp/testsuite/Makefile.am

@@ -25,6 +25,7 @@ testSignature_LDADD = ../src/libycp.la ../src/libycpvalues.la ../../liby2/src/li
 PACKAGE=libycp
 
 AUTOMAKE_OPTIONS = dejagnu
+RUNTEST = Y2DISABLELANGUAGEPLUGINS=1 runtest
 
 clean-local:
 	rm -f tmp.err.* tmp.out.* ycp.log ycp.sum site.exp libycp.log libycp.sum site.bak log.tmp