bos: Fix Windows import of afsconf_SawCell

IBM created a global variable 'afsconf_SawCell' in the kauth package
and manipulated its value from within bos.c as part of the calling
of ka_Init().  Patchset d52398940d58ccdba4114a9975762f48cc24ad15
exported afsconf_SawCell from afsauthent.dll since bos.exe is built
pthreaded.  It was previously mixing pthread and not-pthread libraries
to access the variable.

Unfortunately, the export was declared as a function pointer instead
of DATA.  Importing a DATA element from a library also requires that
the variable be __declspec(dllimport).   The use of afsconf_SawCell
needs to be replaced but in the meantime fix the import so that bos.exe
can start without crashing.

Change-Id: Ic780971b55d64e41e1ba9627cdeadd6c27c451fb
Reviewed-on: http://gerrit.openafs.org/10054
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>