exp10.3: Before glibc 2.19, exp() did not give ERANGE error on underflow

http://sources.redhat.com/bugzilla/show_bug.cgi?id=6787

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
ilogb.3: Since glibc 2.16, ilogb() does correctly diagnore domain errors

Reported-by: Will Newton <will.newton@linaro.org>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
tgamma.3: Since glibc 2.18, errno is correctly set to EDOM when (x == -infinity))

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
standards.7: tfix

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>