man: various cleanup

Change-Id: I9130e7d10ae42e894923097a7c97da802eb0d8c3
Reviewed-on: https://plan9port-review.googlesource.com/2962
Reviewed-by: Russ Cox <rsc@swtch.com>

man/man1/awk.1

@@ -546,10 +546,10 @@ There are no explicit conversions between numbers and strings.
 To force an expression to be treated as a number add 0 to it;
 to force it to be treated as a string concatenate
 \&\fL""\fP to it.
-.br
+.PP
 The scope rules for variables in functions are a botch;
 the syntax is worse.
-.br
+.PP
 UTF is not always dealt with correctly,
 though
 .I awk