DEVEL15-dafs-drop-volheaders-20080925

DEVEL15-dafs-drop-volheaders-20080925

LICENSE IPL10
FIXES 117470

Under certain demand salvage scenarios, it is possible for a stale header
to remain cached with the needsSalvaged flag asserted. Although this will
not affect clients accessing the volume over afsint, it is an issue for
volser clients. VAttachVolumeByName in volser will always attempt to pull
the header over FSSYNC before doing a disk read, under the assumption that
a cached entry in the fileserver will be more current than what is on
disk. This patch causes the fileserver to aggresively invalidate disk
header cache entries when a salvage is in-progress.

(cherry picked from commit 1659861640035f5405429194e72665839cff3720)