such as sh -c 'echo `echo foo`' .
The memory allocated with ckmalloc() at
parser.c:1349:readtoken1() (search for "done:" label)
was never freed.
I changed this to use 'string stack' framework of Ash.
Note that a string on string stack is properly freed on
exception and end of command parsing, and no explicit free
or signal handlings required.
See TOUR for an overview, and memalloc.[ch] for details
of string stack.
ef88b5d2bd