hdf5_der

Checkin of mods to renable test/page_buffer.c and fix outstanding issues,
specifically:

1) Reinserted code in src/H5Fint.c to start page buffer on file open

2) Reinsertion of code in test/Makefile.am to build and run
   test/page_buffer

3) Numerous minor mods test/page_buffer.c:

   a) adjustements to code to allow for the load / insertion of pages
      into the page buffer on file open / create.

   b) added header comments to most functions in test/page_buffer.c

   c) added white space to improve readability of code.

Tested serial, serial/check-vfd, serial/production, parallel,
       parallel/production on Jelly