smatch scan: fix various warningss found using smatch

smatch scan: fix various warningss found using smatch

entry.c:396 load_entry() info: redundant null check on e->pwd calling free()
entry.c:398 load_entry() info: redundant null check on e->cmd calling free()

/usr/include/bits/fcntl.h:48:10: warning: preprocessor token O_NOFOLLOW redefined
macros.h:136:9: this was the original definition

security.c:98:44: warning: non-ANSI function declaration of function 'cron_restore_default_security_context'
crontab.c:439:29: warning: non-ANSI function declaration of function 'tmp_path'

Signed-off-by: Sami Kerola <kerolasa@iki.fi>