rename afs/assert.h to afs/afs_assert.h

rename afs/assert.h to afs/afs_assert.h

provide a private assert header which does not
pollute the normal namespace for the assert header.

further changes will modify pthread operations to not use
generic assert as a "did it work", which breaks if NDEBUG is set

(cherry picked from commit 78502b61b3e8b288ce6fec1f66d14d7e2431642a)
Reviewed-on: http://gerrit.openafs.org/2995
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: Derrick Brashear <shadow@dementia.org>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Change-Id: Iac34946f9de773ea7489cd75edba220bca2158e3
Reviewed-on: http://gerrit.openafs.org/3172
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>