Review request for 6916217: make/modules/Makefile requires ALT_JDK_IMPORT_PATH

[Mandy Chung]

Fix for 6916217: make/modules/Makefile requires ALT_JDK_IMPORT_PATH

Webrev at:
    http://cr.openjdk.java.net/~mchung/6916217/webrev.00/

This fix addresses two problems:
1) A full jdk build would never need a ALT_JDK_IMPORT_PATH. Fix the 
make/modules/Makefile to build modules if ALT_JDK_IMPORT_PATH not set.

2) ClassAnalyzer is using the com.sun.tools.classfile library from the 
langtools repository.  We want to always use the latest version from the 
langtools repository, if exists, as the tool should be synchronized with 
any classfile API change.  For partial forest build where langtools 
doesn't exist, it will use the build outputdir that imports the 
tools.jar from JDK_IMPORT_PATH.

Thanks
Mandy