40068: Abort execution when setuid/setgid fail.

The incumbent code would print an error message and continue execution
with the previous uid/gid values, not even setting lastval:

    % UID=42 id -u; echo $?
    zsh: failed to change user ID: operation not permitted
    1000
    0
    %

3 files changed, 17 insertions, 4 deletions

diff --git a/ChangeLog b/ChangeLog
index 20574d17e..eb29a06cb 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,8 @@
 2016-12-03  Daniel Shahaf  <d.s@daniel.shahaf.name>
 
+	* 40068: Src/params.c, Test/B02typeset.ztst: Abort execution
+	when setuid/setgid fail.
+
 	* 40067: Src/Zle/comp.h, Src/Zle/complete.c, Src/params.c:
 	internal: Document 'cmatcher', parse_cmatcher(), 'comptoend',
 	unsetparam_pm(), and getindex().
diff --git a/Src/params.c b/Src/params.c
index 21a910190..c64d7486b 100644
--- a/Src/params.c
+++ b/Src/params.c
@@ -4077,7 +4077,7 @@ uidsetfn(UNUSED(Param pm), zlong x)
 {
 #ifdef HAVE_SETUID
     if (setuid((uid_t)x))
-	zwarn("failed to change user ID: %e", errno);
+	zerr("failed to change user ID: %e", errno);
 #endif
 }
 
@@ -4098,7 +4098,7 @@ euidsetfn(UNUSED(Param pm), zlong x)
 {
 #ifdef HAVE_SETEUID
     if (seteuid((uid_t)x))
-	zwarn("failed to change effective user ID: %e", errno);
+	zerr("failed to change effective user ID: %e", errno);
 #endif
 }
 
@@ -4119,7 +4119,7 @@ gidsetfn(UNUSED(Param pm), zlong x)
 {
 #ifdef HAVE_SETUID
     if (setgid((gid_t)x))
-	zwarn("failed to change group ID: %e", errno);
+	zerr("failed to change group ID: %e", errno);
 #endif
 }
 
@@ -4140,7 +4140,7 @@ egidsetfn(UNUSED(Param pm), zlong x)
 {
 #ifdef HAVE_SETEUID
     if (setegid((gid_t)x))
-	zwarn("failed to change effective group ID: %e", errno);
+	zerr("failed to change effective group ID: %e", errno);
 #endif
 }
 
diff --git a/Test/B02typeset.ztst b/Test/B02typeset.ztst
index 6d85a63fe..9c56c7e5e 100644
--- a/Test/B02typeset.ztst
+++ b/Test/B02typeset.ztst
@@ -711,3 +711,13 @@
   typeset isreadonly=still
 1:typeset returns status 1 if setting readonly variable
 ?(eval):2: read-only variable: isreadonly
+
+  if (( UID )); then
+    UID=$((UID+1)) date; echo "Status is printed, $?"
+  else
+    ZTST_skip="cannot test setuid error when tests run as superuser"
+  fi
+0:when cannot change UID, the command isn't run
+# 'date' did not run.
+>Status is printed, 1
+?(eval):2: failed to change user ID: operation not permitted