* configure.ac (AC_CHECK_HEADERS): Add process.h.
	(checkfuncs): Add dup3, spawnve, spawnvpe; sort the list.
	(AC_CHECK_FUNCS): Add dup3, spawnve, spawnvpe.
	* configure, config.in: Rebuild.
	* pex-unix.c [HAVE_SPAWNVE] (pex_unix_exec_child): New function.
	[HAVE_SPAWNVE] (save_and_install_fd, restore_fd): New functions.

From-SVN: r166339