Fix x86_64 / x86 powl inaccuracy for integer exponents (bug 19848).

Fix x86_64 / x86 powl inaccuracy for integer exponents (bug 19848).

Bug 19848 reports cases where powl on x86 / x86_64 has error
accumulation, for small integer exponents, larger than permitted by
glibc's accuracy goals, at least in some rounding modes.  This patch
further restricts the exponent range for which the
small-integer-exponent logic is used to limit the possible error
accumulation.

Tested for x86_64 and x86 and ulps updated accordingly.

	[BZ #19848]
	* sysdeps/i386/fpu/e_powl.S (p3): Rename to p2 and change value
	from 8 to 4.
	(__ieee754_powl): Compare integer exponent against 4 not 8.
	* sysdeps/x86_64/fpu/e_powl.S (p3): Rename to p2 and change value
	from 8 to 4.
	(__ieee754_powl): Compare integer exponent against 4 not 8.
	* math/auto-libm-test-in: Add more tests of pow.
	* math/auto-libm-test-out: Regenerated.
	* sysdeps/i386/i686/fpu/multiarch/libm-test-ulps: Update.
	* sysdeps/x86_64/fpu/libm-test-ulps: Likewise.