Fix __ASSUME_PREADV and __ASSUME_PWRITEV for Alpha and MicroBlaze (bug 16649).

Reviewing (for all architectures, with a baseline kernel version of
2.6.32) the kernel support for features for which __ASSUME_* macros
would be affected by a move to 2.6.32 as minimum kernel version showed
up that __ASSUME_PREADV and __ASSUME_PWRITEV were wrongly defined for
MicroBlaze (despite the corresponding syscall table entries not being
wired up in the kernel) and Alpha for 2.6.30 and above (although the
support on Alpha was added in 2.6.33).  This patch makes the
kernel-features.h files undefine those macros for appropriate
versions.

	[BZ #16649]
	* sysdeps/unix/sysv/linux/alpha/kernel-features.h
	[__LINUX_KERNEL_VERSION < 0x020621] (__ASSUME_PREADV): Undefine.
	[__LINUX_KERNEL_VERSION < 0x020621] (__ASSUME_PWRITEV): Likewise.
	* sysdeps/unix/sysv/linux/microblaze/kernel-features.h
	(__ASSUME_PREADV): Undefine.
	(__ASSUME_PWRITEV): Likewise.
nscd: also invalidate netgroup cache on reload
Use ALL_RM_TEST for more libm tests.

Continuing the move to using ALL_RM_TEST for tests in libm-test.inc,
this patch converts the tests of fdim, ldexp and scalb.  fdim and
scalb are cases where tests could depend on the rounding mode though
none of the present test inputs do; ldexp is such a case where the
function is equivalent to scalbn (for binary floating point) and the
tests used were a subset of those for scalbn, so this patch makes
ldexp testing use the scalbn tests, as done for other cases of libm
function aliases.

Tested x86_64 and x86.

	* math/libm-test.inc (fdim_test): Use ALL_RM_TEST.
	(ldexp_test_data): Remove.
	(ldexp_test): Move to after scalbn_test.  Use ALL_RM_TEST with
	scalbn_test_data.
	(scalb_test): Use ALL_RM_TEST.