pg_basebackup: stylistic adjustments

The most user-visible part of this is to change the long options
--statusint and --noloop to --status-interval and --no-loop,
respectively, per discussion.

Also, consistently enclose file names in double quotes, per our
conventions; and consistently use the term "transaction log file" to
talk about WAL segments.  (Someday we may need to go over this
terminology and make it consistent across the whole source code.)

Finally, reflow the code to better fit in 80 columns, and have pgindent
fix it up some more.