Do the required flush when the last reference to a cache stripe is released.

Do the required flush when the last reference to a cache stripe is released.
The installer now completes given enough ram in NEWCC=1, and writes an
understandable FS.  There's at least one more problem preventing the
resulting installation from booting however.
Fix a bug in rmap where we were checking the next (unfortunately named
current) rmap for a segment membership.
Fix a mistake in cache trim.
#ifdef detection of DirectMapping in section in NEWCC mode in page out.

svn path=/trunk/; revision=50110