Improve evaluation of relationals with -oo if "other" arg is positive

fixes #8449
Merge pull request #8460 from skirpichev/8449-fix

Improve evaluation of relationals with -oo if "other" arg is nonnegative
Corrected as_leading_term in sinh, tanh and coth

Replaced the output with x, x and 1/x respectively and added tests.
as_leading_term method of acosh and acoth corrected

Output changed to I*pi/2, tests added and similar tests
put together to save lines.