Check for duplicate library name.requi
	* standard/require.java (importDefinitions): Check if imported
	source file actually defines the required module.

        * Compilation.java (subModuleMap): New field.
       
	* aux-libs.scm: New file, defined two libraries.
	* lib-impsrc1.scm: New test of import-from-source of aux-libs.scm
	* lib-impsrc2.scm: new test of bad import.
	* lib-dup.scm: New test of file with duplicate libraries.
	* Makefile.am: Update accordingly.