podwrapper: Remove =encoding from input files and add it back in podwrapper.

This changes podwrapper so that the input (POD) files should not
contain an =encoding directive.  However they must be UTF-8.
Podwrapper then adds the '=encoding utf8' directive back during final
generation.

This in particular avoids problems with nested =encoding directives in
fragments.  These break POD, and are undesirable anyway.

podwrapper.pl.in

@@ -31,8 +31,6 @@ use File::Basename;
 # https://www.redhat.com/archives/libguestfs/2013-May/thread.html#00088
 eval { $Text::Wrap::huge = "overflow" };
 
-=encoding utf8
-
 =head1 NAME
 
 podwrapper.pl - Generate libguestfs documentation from POD input files
@@ -291,6 +289,12 @@ foreach (@verbatims) {
         if $content eq $oldcontent;
 }
 
+# There should be no =encoding line present in the content (we will add one).
+die "$progname: $input: =encoding must not be present in input\n"
+    if $content =~ /^=encoding/m;
+
+$content = "=encoding utf8\n\n$content";
+
 if ($strict_checks) {
     # Verify sections present / not present.
     die "$progname: $input: missing AUTHOR or AUTHORS section\n"