Italicize "follow" in [basic.lookup.general]/2

[t3nsor]

[basic.lookup.general]/2 is the definition of "follow", not the definition of "program point". "follow" should be italicized to make this clear.

[t3nsor]

@AlisdairM suggests that "follow" is an overly general term to be grabbing here, so perhaps we should also clarify that the definition applies only to this single paragraph.