#2099 `set term tikz help` doesn't honor `PAGER`

[Eisuke Kawashima]

Version: 5.2.5
OS: Debian 9.5

On a Unix-like system, PAGER environment variable is used to view help, e.g. help tikz.
However, set term tikz help does not honor PAGER, i.e. shows the help as if PAGER is not set.