hdf5_msb

[svn-r15451] Purpose: Fix various problems that were occurring when using mounted files.

Description:
Moved mount table from top file structure to shared file structure.  Moved
parent out of mount table and back into top file structure.  Mounted files can
now be accessed from any handle of the parent file.  Changes to how files are
closed.  Stricter cycle checking on mounted files.  Removed unused function
H5F_has_mount().

Tested:
committest in 1.8 branch.  Committing now due to the urgency of the fix.  No
changes here are specific to the trunk, but I will keep an eye on the daily
tests.