vchoi_fork

[svn-r13618] Modified metadata cache to support multiple read only protects of 
cache entries.  Added test code to test the new feature.  Also some 
minor cleanum

h5committested -- passed on copper and sol.  Failed on osage with 
a configuration error that appears unrelated to my changes.  Serial
test (debug mode) passes on Phoenix (Linux x86 2.6 kernel), so I 
went ahead with the checkin.