Use sigjmp_buf with sig{set,long}jmp, not jmp_buf

Patch from Ivo Raisr on BZ#331257


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13812 a5019735-40e9-0310-863c-91ae7b9d1cf9
Use pclose instead of fclose to close pipes opened with popen, which
also allows us to drop the loop that was supposed to give the child a
chance to exit as the pclose will wait properly for the child.

Fix from Ivo Raisr on BZ#331255


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13813 a5019735-40e9-0310-863c-91ae7b9d1cf9