Fix scripts for environments where "set -ux" carries over

Issue 5013: Fix scripts for environments where "set -ux" carries over

Normally, in Bourne shell scripts,
"set -ux" does not carry over to child processes.
However, under some conditions, it carries over to child processes.
(E.g. environment variable SHELLOPTS exists.)

If "set -ux" in smart-autogen.sh carries over to the child processes,
autoconf fails.

In order to avoid the issue,
this commit makes smart-autogen.sh and smart-configure.sh use
"set +ux" to cancel the effect of "set -ux"
just before invoking the child process.

Likewise, this commit also removes "set -e"
for avoiding "set -e" carrying over, and adds alternative error handling.

[lemzwerg, 2016-12-16 17:49:07]

LGTM.

[trueroad, 2016-12-22 11:58:25]

I've pushed to staging.

commit d73ef0f31f2e154633da4a763b9a20a13b920ca2
Issue 5013: Fix scripts for environments where "set -ux" carries over