* sysdeps/unix/sysv/linux/syscalls.list: Add __pipe2 alias.
* io/pipe2.c: Likewise.
* sysdeps/unix/sysv/linux/kernel-features.h: Define __ASSUME_PIPE2
instead of __ASSUME_PACCEPT.
* include/unistd.h: Declare __have_pipe2.
* libio/iopopen.c: Implement "e" flag.
* libio/Makefile (tests): Add tst-popen1.
* libio/tst-popen1.c: New file.