* tests/test_driver.pl: Preserve the LSAN_OPTIONS variable.
* tests/scripts/targets/ONESHELL: Don't set a local variable.
* tests/scripts/functions/let: Test empty let variable.
* src/posixos.c (osync_parse_mutex): Free existing osync_tmpfile.
* src/misc.c (get_tmpfd): Set umask() before invoking mkstemp().
* src/ar.c (ar_parse_name): Check invalid name (shouldn't happen).
* src/function.c (define_new_function): Free previous function entry
when replacing it with a new one.
* src/job.c (child_execute_job): Initialize pid for safety.
(construct_command_argv_internal): In oneshell mode ensure that the
returned argv has the right format (0th element is a pointer to the
entire buffer).

Add a new function $(let ...) which allows lexically scoped variables.

* NEWS: Add information on this feature.
* doc/make.texi (Let Function): Document the 'let' function.
* src/function.c (func_let): Create the 'let' built-in function.
* tests/scripts/functions/let: Test the 'let' built-in function.