Expand PPID on first use

[James Manger]

It would be helpful to expand the acronym PPID on first use. In section 2, 2nd paragraph, start as follows:

“If a pairwise pseudonymous identifier (PPID) was used to obtain the OpenID 2.0 Identifier…”

[John Bradley]

Make the change

[Edmund Jay]

fixes #959 - Migration - Expand PPID on first use

→ <<cset f7011a1bc0b4>>