fetch(1): Fix style

Fix style problems introduced in r367141:

• s/Ql/Pa/ for file names
• Break line properly in macro
• Properly generate back slash character

Not bumping .Dd

Reported by: xtouqh@icloud.com, steffen@sdaoden.eu
Approved by: 0mp@
Differential Revision: https://reviews.freebsd.org/D26946