vchoi_fork

[svn-r9761] Purpose:
Bug fix.

Description:
threadsafe test (ttsafe) would seg-fault if --disable-production --enable-debug
mode is used.  Reason was that the fstack.nused field was not initialized
when created.

Solution:
Init new fstack.nused with 0.

Platforms tested:
Tested in mir, using development/debug mode.
Did not "h5committested" as change is trivial and limited to threadsafe mode.