In preparation for 10.3-RELEASE, revert r296976, i. e. the merge of

In preparation for 10.3-RELEASE, revert r296976, i. e. the merge of
r296416 (head) and r296969 (stable/10) respectively. With SAVESIGVEC
enabled, csh(1) and tcsh(1) leak signal masks after spawning external
commands. This causes strange effects like for example SIGTERM not
being delivered to rc(8) scripts on shutdown albeit these use sh(1),
if csh(1) or tcsh(1) are used as login shell of root. As such r296976
causes way more problems than it solves.
It is anticipated that a proper changeset for the original problem
will be issued as an Errata Notice post-10.3-RELEASE.

PR:		208132
Approved by:	re (gjb)

git-svn-id: svn://svn.freebsd.org/base/releng/10.3@297204 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f